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Biomedical subjects

A Bäcker

Publications and source records attributed to A Bäcker.

At least 19 recordsLinked to original sources
PubMed2006

Nanowires with surface disorder: giant localization lengths and quantum-to-classical crossover.

We investigate electronic quantum transport through nanowires with one-sided surface roughness. A magnetic field perpendicular to the scattering region is shown to lead to exponentially diverging localization lengths in the quantum-to-classical crossover regime. This effect can be quantitatively accounted for by tunneling between the regular and the chaotic components of the underlying mixed classical phase space.

Journal Article↗
PubMed2006

Renal endothelin system and excretory function in Wistar-Kyoto and Long-Evans rats.

AIM: The role of the kidney endothelin system in the renal regulation of fluid and electrolyte excretion was investigated in Wistar-Kyoto (WKY) and Long-Evans (LE) rats in which we found previously marked differences in the renal excretory responses to endothelin A receptor blockade. METHODS: The selective endothelin A and B receptor antagonists BQ-123 (16.4 nmol kg(-1) min(-1)) and BQ-788 (25 nmol kg(-1) min(-1)) were infused i.v. for 50 min in conscious chronically instrumented WKY and LE rats and their renal function and renal endothelin system were studied. RESULTS: Without effects on glomerular filtration rate or renal blood flow, BQ-123 and BQ-788 decreased by more than 50% (P < 0.01) both urine flow rate and electrolyte excretion in WKY rats but only urine flow rate (P < 0.05) in LE rats. Endothelin-1 content, preproET-1/GPDH mRNA ratio, B(max) and K(d) of total endothelin receptors in renal cortex did not differ between the two strains. In contrast, plasma endothelin-1 concentration (0.58 +/- 0.04 vs. 1.05 +/- 0.01 femtomol mL(-1); P < 0.01), renal papillary ET-1 concentration (68 +/- 5 vs. 478 +/- 62 fmol mg(-1) protein; P < 0.01) and preproET-1/GPDH mRNA ratio (0.65 +/- 0.09 vs. 0.88 +/- 0.05; P < 0.05) as well as total endothelin receptor number in renal papilla (B(max) 5.3 +/- 0.4 vs. and 9.0 +/- 1.2 pmol mg(-1) protein; P < 0.05) were markedly lower in LE than in WKY rats. In vitro studies showed that in both strains ET(B) receptors on renal cortical membranes amounted between 65% and 67% and on papillary membranes between 85% and 88%. CONCLUSION: The present data show that the selective ET(A) or ET(B) receptor blockade differentially affects tubular water and salt handling, which becomes apparent in conditions of low renal papillary endothelin receptor number and tissue endothelin-1 concentration.

Animals↗
PubMed2005

Direct allorecognition promotes activation of bystander dendritic cells and licenses them for Th1 priming: a functional link between direct and indirect allosensitization.

T-cell sensitization to indirectly presented alloantigens (indirect pathway of allorecognition) plays a critical role in chronic rejection. The usual very efficient priming of such self-restricted, T helper type 1 (Th1)-deviated CD4+ T cells obviously conflicts with the fact that allogeneic MHC molecules are poorly immunogenic per se. The aim of the present study is to elucidate whether direct allosensitization induces production of inflammatory mediators that may affect recruitment and activation of immature bystander (host) dendritic cells (DC). These potential mechanisms were studied in vitro by conducting primary allogeneic mixed leucocyte reactions (MLR), mimicking the priming phase in secondary lymphoid organs, and secondary MLR, mimicking the effector phase within the graft. Primary, and particularly secondary, MLR supernatants were found to contain high levels of monocyte/immature DC-recruiting CC chemokines and pro-inflammatory cytokines. Exposure of immature DC to primary or secondary MLR supernatants was found to upregulate CD40 expression and further enhanced lipopolysaccharide-induced interleukin-12 (IL-12) p70 production. Secondary MLR supernatants additionally induced upregulation of CD86 and deviated allogeneic T-cell responses towards Th1 (enhanced interferon-gamma production without concomitant induction of detectable IL-4 or IL-10 production). These findings indicate that direct allorecognition may act as a Th1-deviating adjuvant for indirect allosensitization.

Antigen Presentation↗
PubMed2004

Poincare Husimi representation of eigenstates in quantum billiards.

For the representation of eigenstates on a Poincare section at the boundary of a billiard different variants have been proposed. We compare these Poincare Husimi functions, discuss their properties, and based on this select one particularly suited definition. For the mean behavior of these Poincare Husimi functions an asymptotic expression is derived, including a uniform approximation. We establish the relation between the Poincare Husimi functions and the Husimi function in phase space from which a direct physical interpretation follows. Using this, a quantum ergodicity theorem for the Poincare Husimi functions in the case of ergodic systems is shown.

Journal Article↗
PubMed2004

Chronic endothelin receptor blockade reduces end-organ damage independently of blood pressure effects in salt-loaded heterozygous Ren-2 transgenic rats.

The present study was performed to evaluate the role of an interaction between the endothelin (ET) and the renin-angiotensin systems (RAS) in the development and maintenance of hypertension and in hypertension-associated end-organ damage in heterozygous male and female transgenic rats harboring the mouse Ren-2 renin gene (TGR). Twenty-eight days old heterozygous TGR and age-matched transgene-negative normotensive Hannover Sprague-Dawley rats (HanSD) were randomly assigned to groups with normal-salt (NS) or high-salt (HS) intake. Nonselective ET(A)/ET(B) receptor blockade was achieved with bosentan (100 mg.kg(-1).day(-1)). All male and female HanSD as well as heterozygous TGR on NS exhibited 100 % survival rate until 180 days of age (end of experiment). HS diet in heterozygous TGR induced a transition from benign to malignant phase hypertension. The survival rates in male and in female heterozygous TGR on the HS diet were 46 % and 80 %, respectively, and were significantly improved by administration of bosentan to 76 % and 97 %, respectively. Treatment with bosentan did not influence either the course of hypertension (measured by plethysmography in conscious animals) or the final levels of blood pressure (measured by a direct method in anesthetized rats) in any of the experimental groups of HanSD or TGR. Administration of bosentan in heterozygous TGR fed the HS diet markedly reduced proteinuria, glomerulosclerosis and attenuated the development of cardiac hypertrophy compared with untreated TGR. Our data show that the ET receptor blockade markedly improves the survival rate and ameliorates end-organ damage in heterozygous TGR exposed to HS diet. These findings indicate that the interaction between the RAS and ET systems plays an important role in the development of hypertension-associated end-organ damage in TGR exposed to salt-loading.

Administration, Oral↗
PubMed2002

Hyperosmolality induced by betaine or urea stimulates endothelin synthesis by differential activation of ERK and p38 MAP kinase in MDCK cells.

We have previously shown that cultured porcine inner medullary collecting duct cells produce endothelin (ET) which suppressed arginine vasopressin (AVP)-induced cyclic adenosine monophosphate (cAMP) generation in an autocrine/paracrine feedback-like fashion. Moreover, hyperosmolality, e.g. induced by sodium chloride and urea, stimulated ET synthesis. Since others showed that hyperosmolality also activates mitogen-activated protein (MAP) kinases and that p38 MAP kinase facilitates cellular influx of betaine to protect the cell from high extracellular solute (urea) concentrations, we were tempted to investigate a potential interaction of MAP kinases with ET production in cultured MDCK cells in response to extracellular hyperosmolality induced by betaine and urea, respectively. Increased extracellular tonicity (602 +/- 8 vs. control of 323 +/- 3 mosmol/kg H(2)O) induced by betaine stimulated ERK and, more strongly, p38 kinase activity at 0.5-2 h of incubation with a rise in ET-1 synthesis to 1,713 +/- 68 vs. 378 +/- 51 fmol/mg protein/24 h under control conditions (p < 0.01). The p38 MAP kinase inhibitor SB203580 suppressed the rise in betaine-induced ET-1 synthesis by 91% to 494 +/- 38 fmol/mg protein/24 h, whereas the MEK/ERK inhibitor U0126 suppressed it moderately by 34%. Hypertonicity induced by urea moderately stimulated ERK but not p38 MAP kinase activity at 0.5-2 h and at 24-48 h and resulted in a modest rise in ET-1 synthesis to 681 +/- 61 fmol/mg protein/24 h (p < 0.05) which was significantly suppressed by U0126 to 484 +/- 16 fmol/mg protein/24 h. These results suggest that a functional interaction between the MAP kinases ERK and p38 MAP kinase and ET-1 synthesis is involved in betaine's protection of MDCK cells in vitro which may represent an in vivo mechanism of protection from hyperosmotic stress induced by high extracellular solute concentrations.

Animals↗
PubMed2002

Role of nNOS in regulation of renal function in hypertensive Ren-2 transgenic rats.

The present study was performed to evaluate the role of neuronal nitric oxide synthase (nNOS)-derived nitric oxide (NO) during the developmental phase of hypertension in transgenic rats harboring the mouse Ren-2 renin gene (TGR). The first aim of the present study was to examine nNOS mRNA expression in the renal cortex and to assess the renal functional responses to intrarenal nNOS inhibition by S-methyl-L-thiocitrulline (L-SMTC) in heterozygous TGR and in age-matched transgene-negative Hannover Sprague-Dawley rats (HanSD). The second aim was to evaluate the role of the renal sympathetic nerves in mediating the renal functional responses to intrarenal nNOS inhibition. Thus, we also evaluated the effects of intrarenal L-SMTC administration in acutely denervated TGR and HanSD. Expression of nNOS mRNA in the renal cortex was significantly increased in TGR compared with HanSD. Intrarenal administration of L-SMTC decreased the glomerular filtration rate (GFR), renal plasma flow (RPF) and sodium excretion and increased renal vascular resistance (RVR) in HanSD. In contrast, intrarenal inhibition of nNOS by L-SMTC did not alter GFR, RPF or RVR and elicited a marked increase in sodium excretion in TGR. This effect of intrarenal L-SMTC was not observed in acutely denervated TGR. These results suggest that during the developmental phase of hypertension TGR exhibit an impaired renal vascular responsiveness to nNOS derived NO or an impaired ability to release NO by nNOS despite enhanced expression of nNOS mRNA in the renal cortex. In addition, the data indicate that nNOS-derived NO increases tubular sodium reabsorption in TGR and that the renal nerves play an important modulatory role in this process.

Analysis of Variance↗
PubMed2001

Endothelin synthesis and receptors in porcine kidney.

As insufficient information on the endothelin (ET) system in the porcine kidney is available at present, we investigated renal ET-1 synthesis and ET receptors in this species. Because ET specifically affects renal and glomerular haemodynamics and distal tubular reabsorption, we studied ET-1 synthesis in isolated glomeruli and in inner medullary collecting duct (IMCD) cells and preproET-1 mRNA in renal cortex, isolated glomeruli and papillary tissue. In addition, we characterized density and properties of ET receptors in membranes from isolated glomeruli and papillary tissue. In contrast to isolated IMCD cells, which synthesized 120 +/- 11 fmol h(-1) mg-1 protein of ET-1, no such synthesis was found with isolated glomeruli in our assay system. Nevertheless, with RT-PCR preproET(-1) mRNA was clearly present in renal cortex and glomeruli as well as in papillary tissue. Glomerular membranes were found to have ET receptors with Bmax of 1.6 +/- 0.2 pmol mg-1 protein and Kd of 311 +/- 33 pmol L(-1). Using BQ-123 (10-5 M), a specific blocker of ETA receptors, we found that 58% of total receptors are ETA receptors. Thus, presumably 42% are ETB receptors (Bmax 0.7 +/- 0.1 pmol mg-1 protein; Kd 429 +/- 110 pmol L(-1)). Bosentan (10-5 M), an ETA- and ETB-receptor antagonist, blocked all ET receptors in glomerular membranes. Papillary membranes showed ET receptors with Bmax of 2.1 +/- 0.2 pmol mg-1 protein and Kd of 137 +/- 11 pmol L(-1). In the presence of BQ-123 (10-5 M) we found that all receptors are ETB receptors (Bmax 2.3 +/- 0.4 pmol mg-1 protein; Kd 162 +/- 25 pmol L(-1)). Bosentan (10-5 M) again blocked all ET receptors in papillary membranes, thus confirming our previous finding that IMCD cells possess high-affinity ETB receptors mediating the diuretic effects of ET. Thus, in the porcine kidney the ET system may act in an autocrine/paracrine manner at the glomerular as well as at the IMCD level.

Animals↗
PubMed2000

Inhibitors of Na-K-ATPase in human urine: effects of ouabain-like factors and of vanadium-diascorbate on calcium mobilization in rat vascular smooth muscle cells: comparison with the effects of ouabain, angiotensin II, and arginine-vasopressin.

Endogenous ouabain-like factors (OLF) may play a role in the pathogenesis of volume-dependent hypertension by raising intracellular free calcium ([Ca2+]i) as a consequence of inhibition of the sodium pump. In previous studies we described the presence of two low molecular (Mr approximately equals 400) inhibitors of Na-K-ATPase in human urine, ie, a more polar OLF-1 and a more apolar OLF-2. We subsequently identified the active compound in OLF-2 as vanadium (V(IV))-diascorbate (Mr 416). OLF-1, OLF-2, and V-diascorbate inhibited dose-dependently porcine Na-K-ATPase in vitro. In the present study we investigated the effects of urinary OLF-1, OLF-2, and V-diascorbate on calcium mobilization, ie, on [Ca2+]i in cultured rat vascular smooth muscle (VSM) cells in comparison to the effects of ouabain, angiotensin II (A II), and arginine-vasopressin (AVP). [Ca2+]i was determined by the fura-2 method. OLF-1 and OLF-2 (each approximately equals 10(-4) mol/L), obtained as single spots by thin-layer chromatography, produced a rise in [Ca2+]i in VSM cells from 45 +/- 7 to 99 +/- 22 and from 48 +/- 9 to 92 +/- 2 nmol/L (each n = 5; P < .05), respectively, after 3 min. V-diascorbate also increased [Ca2+]i slowly and dose-dependently, eg, from 56 +/- 14 to 102 +/- 15 nmol/L at a concentration of 10(-6) mol/L (n = 5; P < .05) after 3 min. A similar slow rise in [Ca2+]i from 53 +/- 10 to 185 +/- 3 nM (n = 5; P < .05) after 3 min was found with ouabain (10(-6) mol/L). As standard vasoconstrictor, All (10(-8) mol/L) rapidly increased [Ca2+]i from 23 +/- 4 to 846 +/- 50 nmol/L (n = 7; P < .01) within 30 sec. This effect was enhanced to 1,389 +/- 161 nM (n = 7; P < .01) when VSM cells were preincubated with V-diascorbate (10(-6) mol/L) for 10 min. AVP (10(-7) mol/L) also rapidly increased [Ca2+]i to 418 +/-11 nmol/L within 30 sec (n = 7; P < .01). This effect was enhanced in the presence of OLF-2 (approximately equals 10(-4) mol/L) or ouabain (10(-6) mol/L) to 523 +/- 14 and 560 +/- 19 nmol/L, respectively (each n = 7); P < .01). The calcium channel blocker verapamil, the intracellular calcium release blocker TMB-8, and the unselective cation channel blocker Ni2+ partly blunted the A II- or AVP-induced rise in [Ca2+]i and prevented the OLF-2- and V-diascorbate-induced increase in [Ca2+]i. Thus, OLF-1, OLF-2 and V-diascorbate, the active component of OLF-2, reveal effects similar to those of ouabain on [Ca2+]i in VSM cells, ie, they produce a slow rise in [Ca2+]i subsequent to inhibition of the sodium pump. The physiologic and pathologic roles of these and additional OLF in body fluid and blood pressure regulation and in hypertension have yet to be evaluated.

Adult↗
PubMed2000

Influence of asimadoline, a new kappa-opioid receptor agonist, on tubular water absorption and vasopressin secretion in man.

AIMS: The purpose of the study was to investigate the effects of asimadoline, a new kappa-opioid agonist, on renal function and on hormones related to body fluid balance as well as its tolerability in healthy subjects. METHODS: In a placebo-controlled, randomised, double-blind crossover design we studied the effects of single oral doses of 1, 5, and 10 mg of asimadoline, in 24 healthy volunteers. Two hour control urine collections were followed by 2 h postdose urine collections and subsequently 2.5% saline was given i.v. at a rate of 0.3 ml min(-1) kg(-1) during another 2 h urine collection. Blood was obtained hourly. Arginine-vasopressin (AVP), atrial natriuretic peptide (alpha-hANP), endothelin (ET-1) and cAMP were determined by r.i.a. or ELISA. RESULTS: GC-MS measurements revealed Cmax values of asimadoline in plasma ranging from 18 ng ml(-1) at the 1 mg dose, 91 ng ml(-1) at the 5 mg dose, to 214 ng ml(-1) at the 10 mg dose after an average of 1.1-1.4 h. Without effects on blood pressure, heart rate, GFR or urine electrolyte excretion, urine volume increased after 1-2 h after administration of 5 and 10 mg asimadoline from 3.3+/-1.3 to 5.6+/-1.4 (P<0.05) and from 3.2 +/-1.6 to 5.5+/-2.2 ml min(-1) (P<0.01), respectively. CH2O rose from 0.2+/-1.5 to 2.0+/-1.6 (P<0.05) and from 0.6+/-1.6 to 3.0+/-1.6 ml min(-1) (P<0.01). Urinary excretion of AVP was suppressed only with the 10 mg dose from 46+/-23 to 25+/-15 fmol min(-1) (P<0.05) without and from 410+/-206 to 181+/-125 fmol min(-1) (P<0.05) with stimulation by 2.5% saline. Plasma AVP was suppressed only by the 10 mg dose of asimadoline in six of eight subjects during the 2.5% saline infusion. Changes in the alpha-hANP or ET-1 systems were not affected by asimadoline. CONCLUSIONS: Asimadoline is diuretic in man after single doses of 5 or 10 mg probably through a direct effect at the renal tubular level. Suppression of AVP secretion was observed only at the highest dose level of 10 mg of asimadoline.

Acetamides↗
PubMed1999

The renal endothelin system in the Prague hypertensive rat, a new model of spontaneous hypertension.

In a new model of spontaneous hypertension, namely the Prague hypertensive rat (PHR), hypertension is transferred with a kidney transplanted from the PHR to its normotensive counterpart (PNR) by an as yet unknown mechanism. One candidate may be endothelin (ET), since this potent vasoconstrictor affects vascular tone, renal haemodynamics and renal excretory function, and all members of this peptide family are located within the kidney and act in an autocrine/paracrine fashion. In the present study we investigated, in the renal tissue of PHRs and PNRs: (1) preproET-1 and preproET-3 mRNAs as well as ET-1 and ET-3 peptide distribution, (2) endothelin-converting enzyme (ECE)-1 mRNA expression, and (3) ET receptors and their characteristics in membranes of glomeruli and papillae. In addition, plasma ET concentration and urinary ET excretion were determined. Quantitative measurements by competitive reverse transcription-polymerase chain reaction revealed ET-1 mRNA levels in the renal cortex from PHRs and PNRs of 1.09+/-0.13 and 1. 29+/-0.18 amol/microgram of total RNA respectively, and in red medulla of 2.72+/-0.82 and 3.30+/-0.68 amol/microgram respectively. In contrast, renal papilla from PHRs showed significantly lower levels of preproET-1 mRNA (1.81+/-0.64 amol/microgram of total RNA, compared with 4.25+/-0.82 amol/microgram in PNRs; each n=5; P<0.05). The ET-1 peptide concentration in papillary tissue was also significantly lower in PHRs than in PNRs (120.2+/-30.8 and 491.3+/-53.4 fmol/mg of protein respectively; n=5; P<0.01), whereas it was similar in cortex and medulla from PHRs and PNRs. The preproET-3 mRNA content in renal tissue was much lower than that of preproET-1 mRNA. It was significantly higher in red medulla from PHRs compared with that from PNRs (0.25+/-0.05 and 0.13+/-0.02 amol/microgram of total RNA respectively; P<0.05), but was similar in papillae of PHRs and PNRs (0.04+/-0.02 and 0.05+/-0.01 amol/microgram respectively; n=5). Cortical preproET-3 mRNA was at the lower limit of detection. Similarly, the ET-3 peptide concentration was slightly but significantly higher in the red medulla of PHRs compared with PNRs (15.4+/-2.0 and 8.8+/-0.8 fmol/mg of protein respectively; n=5; P<0. 05), whereas no differences in ET-3 peptide concentration were found in papillae from PHRs and PNRs. ECE-1 mRNA levels were similar in the renal cortex, red medulla and papillae from PHRs and PNRs, ranging between 0.34+/-0.03 and 0.56+/-0.12 amol/microgram of total RNA. Of the total ET receptors in glomerular membranes, 39% were ETA receptors, whereas papillary membranes contained exclusively ETB receptors. PHRs and PNRs showed similar Bmax and Kd values for ET-1 in renal glomerular membranes (Bmax, 6.5+/-1.3 and 4.9+/-1.2 pmol/mg of protein respectively; Kd, 0.69+/-0.10 and 0.56+/-0.10 nM respectively) and papillary membranes (Bmax, 9.7+/-1.1 and 11.3+/-1. 6 pmol/mg of protein respectively; Kd, 0.30+/-0.04 and 0.42+/-0.07 nM respectively). Plasma ET-1/2 concentrations (10.4+/-1.3 and 12. 2+/-1.2 fmol/ml in PHRs and PNRs respectively) and urinary ET-1 excretion (3.1+/-0.3 and 3.0+/-0.2 pmol/24 h in PHRs and PNRs respectively) were similar in hypertensive and normotensive rats. In summary, although tissue levels of preproET-3 mRNA were very low in the kidney, significantly greater amounts of preproET-3 mRNA and ET-3 peptide were found in medullary tissue from PHRs compared with PNRs, a finding that awaits further investigation. In contrast, the preproET-1 mRNA content and ET-1 peptide concentration were significantly lower in papillary tissue from PHRs compared with PNRs. Decreased synthesis of ET-1, which normally antagonizes the action of [Arg8]vasopressin, may allow increased water (and sodium) reabsorption at the level of the inner medullary collecting duct. This intrinsic defect of the kidney in the PHR may contribute to hypertension in this model, and may transmit high blood pressure on transplantation of the 'hypertensive' kidney i

Actins↗
PubMed1998

Who reads temporal information contained across synchronized and oscillatory spike trains?

Our inferences about brain mechanisms underlying perception rely on whether it is possible for the brain to 'reconstruct' a stimulus from the information contained in the spike trains from many neurons. How the brain actually accomplishes this reconstruction remains largely unknown. Oscillatory and synchronized activities in the brain of mammals have been correlated with distinct behavioural states or the execution of complex cognitive tasks and are proposed to participate in the 'binding' of individual features into more complex percepts. But if synchronization is indeed relevant, what senses it? In insects, oscillatory synchronized activity in the early olfactory system seems to be necessary for fine odour discrimination and enables the encoding of information about a stimulus in spike times relative to the oscillatory 'clock. Here we study the decoding of these coherent oscillatory signals. We identify a population of neurons downstream from the odour-activated, synchronized neuronal assemblies. These downstream neurons show odour responses whose specificity is degraded when their inputs are desynchronized. This degradation of selectivity consists of the appearance of responses to new odours and a loss of discrimination of spike trains evoked by different odours. Such loss of information is never observed in the upstream neurons whose activity is desynchronized. These results indicate that information encoded in time across ensembles of neurons converges onto single neurons downstream in the pathway.

Animals↗
PubMed1998

Effects of urinary ouabain-like factors and vanadium diascorbate on calcium mobilization in porcine inner medullary collecting duct cells: comparison with the effects of ouabain and vasopressin.

It is speculated that ouabain-like factors (OLF) play a role in the pathogenesis of volume-dependent hypertension. In previous studies we isolated a more polar OLF-1 and a more apolar OLF-2 from the urine of healthy subjects after 5 days on a high sodium intake (>400 mmol/day) by gel chromatography (Sephadex G-25 and G-10) and reverse-phase HPLC. We subsequently identified the chemical structure of OLF-2 as vanadium (V(IV)) diascorbate. OLF-1, OLF-2, and vanadium diascorbate inhibited dose-dependently porcine Na-K-ATPase in vitro. Because the inner medullary collecting duct (IMCD) plays a crucial role in the long-term regulation of body fluid volume, in the present study we investigated the effects of urinary OLF-1 and OLF-2, and of vanadium diascorbate in comparison to ouabain and vasopressin (AVP) on calcium mobilization, ie, on free calcium concentration [Ca2+]i, in cultured porcine IMCD cells. [Ca2+]i was determined by the fura-2 method in IMCD cells isolated by hypotonic treatment and density gradient centrifugation from fresh porcine kidneys. Assuming an approximate molecular weight (MW) of 400 for OLF-1 and OLF-2, OLF-1 (10(-4) mol/L) produced a slow increase in [Ca2+]i from 39 +/- 10 to 169 +/- 21 nmol/L (n = 7 ) after 4 min. Similarly, OLF-2 (10(-4) mol/L) resulted in an increase in [Ca2+]i from 74 +/- 20 to 216 +/- 52 nmol/L (n = 7) after 4 min. Vanadium diascorbate (MW 403) dose-dependently increased [Ca2+]i . At a concentration of 10(-6) mol/L it increased [Ca2+]i from 46 +/- 5 to 149 +/- 9 nmol/L (n = 5) after 4 min. A similar slow increase in [Ca2+]i was found with ouabain (10(-6) mol/L), which increased [Ca2+]i from 61 +/- 22 to 180 +/- 29 nmol/L (n = 5) after 4 min in contrast to AVP (10(-7) mol/L), which rapidly increased [Ca2+]i from 48 +/- 10 to 299 +/- 32 nmol/L (n = 4) within 30 sec. Thus, OLF-1, OLF-2, and Vanadium diascorbate, the active component of OLF-2, reveal similar effects as ouabain on IMCD cells, ie, they produce a slow increase in [Ca2+]i as expected from inhibition of Na-K-ATPase. The physiologic or pathologic roles of these and additional OLF in body fluid and blood pressure regulation and in hypertension have yet to be evaluated.

Adult↗
PubMed1997

Effects of erythropoietin on endothelin-1 synthesis and the cellular calcium messenger system in vascular endothelial cells.

A rise in blood pressure is the main side effect of erythropoietin (EPO) treatment in patients with renal anemia. The mechanisms, however, by which EPO may cause hypertension are still unclear. We therefore investigated the effects of EPO on endothelin (ET) synthesis and cytosolic free calcium concentration ([Ca2+]i) in vascular endothelial cells. Porcine endothelial cells were isolated from thoracic aorta, pulmonary artery, and vena cava. Studies were performed with cells of the first subculture. ET concentrations were measured radioimmunologically. Changes in [Ca2+]i were determined with the fluorescent probe fura-2. Cytotoxicity was assessed by sodium 3'-[1-(phenyl-amino-carbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)ben zene sulfonic acid hydrate (XTT) assay. ET synthesis was similar in cells of different vascular origins and was time-dependent, reaching approximately 2 pmol ET/mg protein within 12 h of incubation. EPO (12 to 200 U/mL) stimulated ET release time- and dose-dependently by up to 83.2% (P < .01) within 12 h in the absence of fetal calf serum and heparin. EPO induced an immediate significant rise in [Ca2+]i from 58 +/- 12 nmol/L to 495 +/- 85 nmol/L (P < .01) with a subsequent slow return to 257 +/- 3 nmol/L. During 2 h of incubation, the Ca-ionophore A 23187 (10(-8) mol/L) moderately but significantly stimulated endothelial ET synthesis. However, the Ca-channel blocker verapamil, the intracellular Ca-release blocker TMB-8, and nickel, an unspecific calcium channel blocker, had no consistent effects on [Ca2+]i or ET synthesis. The protein kinase C inhibitor H-7 stimulated basal [Ca2+]i and cellular ET synthesis. The tyrosine kinase inhibitor genistein suppressed the EPO-induced rise in [Ca2+]i and cellular ET synthesis. From these data we conclude that EPO may stimulate ET synthesis in vascular endothelial cells by activation of an EPO-receptor and via intracellular signalling mechanisms that comprise tyrosine kinase activation and a rise in [Ca2+]i. Therefore, the systemic hypertensive effects of EPO may be due at least in part to local stimulation of vascular endothelial ET synthesis via calcium mobilization.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1997

Renal endothelin system in obstructive jaundice: its role in impaired renal function of bile-duct ligated rats.

1. Obstructive jaundice predisposes the kidney to acute renal failure. Endothelin (ET), a potent renal vasoconstrictor and modulator of the tubular action of arginine vasopressin, has been suggested to play a pathogenetic role in acute renal failure. In the present study we therefore investigated renal function and the renal ET system in rats on day 4 after bile-duct ligation (BDL) or sham-operation (SO), without (n = 7 in each group) and with treatment with bosentan, a combined ETA/ETB receptor blocker, (n = 5 in each group). 2. On day 4 after BDL, serum bilirubin had increased to 226 +/- 10 mumol/l (SEM) as compared with 6 +/- 2 mumol/l in SO rats. Endogenous creatinine clearance, an index of glomerular filtration rate, was significantly reduced to 0.7 +/0 0.1 ml min-1 g-1 of kidney weight after BDL as compared with 1.1 +/- 0.1 ml min-1 g-1 of kidney weight after SO (P < 0.05). Bosentan prevented the decrease in glomerular filtration rate (1.0 +/- 0.2 ml min-1 g-1 of kidney weight), as well as polyuria and defective concentrating ability, in BDL rats. 3. Plasma ET concentration on day 4 after surgery (28.2 +/- 1.5 pmol/l) was higher (P < 0.01) in BDL than in SO rats (12.9 +/- 1.5 pmol/l) and rose further in bosentan-treated BDL and SO rats (43.4 +/- 5.1 compared with 21.9 +/- 6.6 pmol/l). Urinary ET excretion was significantly higher in BDL rats than in SO rats (1.58 +/- 0.22 compared with 1.28 +/- 0.18 pmol 24 h-1 100 g-1 of body weight; P < 0.05). 4. ET synthesis by glomeruli isolated from BDL rats was lower [81 +/- 19 fmol h-1 (mg of protein)-1] than that from SO-rats [139 +/- 28 fmol h-1 (mg of protein)-1; P < 0.05], whereas papillary ET synthesis was higher in BDL [10 +/- 3 fmol h-1 (mg of protein)-1] than in SO rats [4 +/- 1 fmol h-1 (mg of protein)-1; P < 0.05]. 5. The results indicate that BDL is associated with increased plasma ET concentration and suppression of GFR. Enhanced renal inner medullary collecting-duct ET synthesis, which is reflected by increased urinary ET excretion, may reduce distal tubular water absorption in BDL rats. Increased circulating and renal papillary ET synthesis may thus contribute to renal dysfunction and predispose the kidney to acute renal failure in obstructive jaundice.

Acute Kidney Injury↗
PubMed1997

Cellular mechanisms of cyclosporine A-associated side-effects: role of endothelin.

Immunosuppressive therapy with cyclosporine A (CsA) may be associated with severe side-effects such as nephrotoxicity and arterial hypertension. The partial reversability of these effects suggests that they are at least in part functional. We examined the effects of CsA on cellular signaling in cultured vascular smooth muscle cells from rat aorta. Intracellular free calcium concentrations ([Ca2+]i) were measured using fura-2. Total cell calcium was measured by atomic absorption and cellular endothelin production was estimated by radioimmunoassay. In the presence of CsA the calcium mobilizing effect of angiotensin (Ang) II was significantly enhanced. While the ETA receptor antagonist BQ 123 did not affect Ang II-induced calcium mobilization, the potentiating effect of CsA on [Ca2+]i was blocked by BQ 123. Preincubation of the cells with cyclosporine (10 micrograms/ml) for 30 minutes increased total cell calcium from 2.6 +/- 0.5 to 6.9 +/- 0.3 nmol/mg protein (P < 0.01). Within 24 hours endothelin production was significantly enhanced in the presence of cyclosporine (52.2 +/- 2.5 vs. 65.9 +/- 2.7 fmol/mg protein, P < 0.05). Therefore, the cyclosporine-induced rise of total cell calcium in smooth muscle cells is associated with an enhanced production of endothelin. We speculate that cyclosporine induced changes of Ca(2+)-kinetics may be mediated by endothelin. These results indicate that endothelin may play a major role in cyclosporine-associated side-effects.

Animals↗
PubMed1996

Calcium entry and 5-HT2 receptor blockade in oliguric ischaemic acute renal failure: effects of levemopamil in conscious rats.

1. Unilateral left renal artery occlusion for 1 h in a group of 8 untreated female Sprague-Dawley rats resulted in oliguric acute renal failure (ARF) persisting for more than 6 h after reflow, i.e. after reperfusion of the kidney by removal of the arterial clamp. In a second group of 8 rats with left unilateral ARF the effects of levemopamil (L), a calcium entry blocker with 5-hydroxytryptamine2 (5-HT2) receptor antagonistic properties, were studied. Rats received L as a continuous infusion (6 mg kg-1 h-1) from 1 h before ischaemia until 6 h after reflow. 2. Endogenous creatinine clearance, an estimate of glomerular filtration rate (GFR), of left ischaemic kidneys of untreated rats was almost completely abolished and urine flow was 0.05 +/- 0.02 and 0.03 +/- 0.01 ml h-1 100 g-1 body weight (body wt.) at 2 and at 6 h of reflow, respectively. In contrast, left ischaemic kidneys of L-treated rats revealed significantly higher GFR (0.10 +/- 0.02 and 0.03 +/- 0.01 ml min-1 g-1 kidney weight (k.wt.); P < 0.01) and urine flow (0.51 +/- 0.05 and 0.15 +/- 0.04 ml h-1 100 g-1 body wt.; P < 0.05) at 2 and 6 h of reflow, respectively. 3. At 6 h of reflow, mitochondria from the cortex of left ischaemic kidneys of untreated rats showed significantly reduced ATP synthesis when compared to right intact kidneys (0.06 +/- 0.02 vs 0.26 +/- 0.02 mumol ATP mg-1 protein min-1 (P < 0.01)). In contrast, in L-treated rats, ATP synthesis of left ischaemic kidneys was largely preserved (0.17 +/- 0.01 mumol ATP mg-1 protein min-1). 4. Ischaemia of left kidneys resulted in a significant decrease in medullary Na-K-ATPase activity to 9.6 +/- 2.4 as compared to 20.4 +/- 3.7 mumol P(i) h-1 mg-1 protein in the intact right kidneys which was not prevented by L (9.4 +/- 2.4 mumol P(i) h-1 mg-1 protein). 5. In untreated rats the calcium content in cortical mitochondria from left ischaemic kidneys had risen 2 fold to 23.0 +/- 1.8 at 6 h of reflow as compared to 12.2 +/- 0.3 nmol mg-1 protein in right intact kidneys (P < 0.01). This rise in mitochondrial calcium was not significantly attenuated by treatment with L (19.9 +/- 1.7 nmol mg-1 protein). 6. The results show that L transiently converted oliguria into non-oliguria during the early phase after reflow in ischaemic ARF, i.e. after reperfusion following 1 h of complete interruption of renal perfusion. The present data suggest indirectly that the 5-HT2-antagonistic properties of L rather than its calcium channel blocking action maintains GFR at low level and protects mitochondrial function early after reflow in this model of ischaemic ARF.

Acute Kidney Injury↗