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A Erik G Persson

Publications and source records attributed to A Erik G Persson.

At least 19 recordsLinked to original sources
PubMed2007

Angiotensin II-nitric oxide interaction in the kidney.

PURPOSE OF REVIEW: The balance of angiotensin II and nitric oxide determines the sensitivity of the tubuloglomerular feedback mechanism, renal vascular resistance and filtration rate. Angiotensin II induces nitric oxide release, but the role of angiotensin II receptors here is not fully understood. Further, the angiotensin II-nitric oxide interaction can be modulated by reactive oxygen species. This review focuses on the angiotensin II-nitric oxide interaction and their modulation by reactive oxygen species in the control of renal blood flow. RECENT FINDINGS: Ideas about the role of angiotensin II type 1 and angiotensin II type 2 receptors are extended by the observation of angiotensin II type 1-mediated nitric oxide release with direct effects on vascular tone, tubuloglomerular feedback and sympathetic neurotransmission. Angiotensin receptors elicit disparate effects on intrarenal circulation. Angiotensin II-nitric oxide interactions are modulated by reactive oxygen species, as shown by angiotensin II type 1-mediated activation of superoxide and depression of antioxidant enzymes leading to reduced nitric oxide concentration - mechanisms that may be also important in angiotensin II-dependent hypertension. SUMMARY: Recent studies show that angiotensin II stimulates the nitric oxide system via angiotensin II type 1 and angiotensin II type 2 receptors, whereas receptors exert different effects on renal and medullary flow. The interaction via angiotensin II type 1 is modulated by reactive oxygen species.

Angiotensin II↗
PubMed2007

Vascular reactivity in arterioles from normal and alloxan-diabetic mice: studies on single perfused islets.

Pancreatic islets possess an autonomous mechanism of blood flow regulation, independent of that of the exocrine pancreas. To study islet vascular regulation without confounding effects of the exocrine blood vessels, we have developed a technique enabling us to isolate single pancreatic islets and then to perfuse them using their endogenous vasculature for distribution of the medium. This made it possible to directly study the vascular reactivity of islet arterioles to different substances. We confirmed that control of islet blood flow is mainly located at the precapillary level. As expected, administration of angiotensin II and l-nitro-arginine methyl ester contracted islet arterioles, whereas nitric oxide and adenosine dilated them. d-glucose, the main insulin secretagogue, had a selective dilating effect on smooth muscle in islet arterioles but not in glomerular afferent arterioles. The response to glucose was amplified in islet arterioles from diabetic animals, indicating enhanced islet blood perfusion in diabetes. This newly developed technique for perfusing isolated pancreatic islets will provide new insights into islet perfusion control and its possible contributions to the pathogenesis of type 2 diabetes.

Angiotensin II↗
PubMed2006

Adenosine restores angiotensin II-induced contractions by receptor-independent enhancement of calcium sensitivity in renal arterioles.

Adenosine is coupled to energy metabolism and regulates tissue blood flow by modulating vascular resistance. In this study, we investigated isolated, perfused afferent arterioles of mice, which were subjected to desensitization during repeated applications of angiotensin II. Exogenously applied adenosine restores angiotensin II-induced contractions by increasing calcium sensitivity of the arterioles, along with augmented phosphorylation of the regulatory unit of the myosin light chain. Adenosine restores angiotensin II-induced contractions via intracellular action, because inhibition of adenosine receptors do not prevent restoration, but inhibition of NBTI sensitive adenosine transporters does. Restoration was prevented by inhibition of Rho-kinase, protein kinase C, and the p38 mitogen-activated protein kinase, which modulate myosin light chain phosphorylation and thus calcium sensitivity in the smooth muscle. Furthermore, adenosine application increased the intracellular ATP concentration in LuciHEK cells. The results of the study suggest that restoration of the angiotensin II-induced contraction by adenosine is attributable to the increase of the calcium sensitivity by phosphorylation of the myosin light chain. This can be an important component of vascular control during ischemic and hypoxic conditions. Additionally, this mechanism may contribute to the mediation of the tubuloglomerular feedback by adenosine in the juxtaglomerular apparatus of the kidney.

Adenosine↗
PubMed2006

Hydronephrosis causes salt-sensitive hypertension in rats.

BACKGROUND: Hypertension is a common disease in the Western world and approximately 5% of all cases are secondary to kidney malfunction. It is not clear whether unilateral hydronephrosis due to partial obstruction affects blood pressure. AIM: The aim of this study was to determine whether hypertension develops and to investigate the effects of different salt diets on the blood pressure in hydronephrotic animals. METHODS: Unilateral partial ureteral obstruction was created in 3-week-old Sprague-Dawley rats. A telemetric device was implanted 4-6 weeks later and blood pressure was measured on normal, low- and high-salt diets. Plasma samples were collected on all diets for renin analysis. RESULTS: All hydronephrotic animals developed hypertension that correlated to the degree of hydronephrosis. The blood pressure increased slowly with time and was salt sensitive. In severe hydronephrosis, blood pressure increased from 118 +/- 5 mmHg on low salt to 140 +/- 6 mmHg on high salt intake, compared to control levels of 82 +/- 2 and 84 +/- 2 mmHg, respectively. Plasma renin concentration was increased in the hydronephrotic group of animals compared to controls on all diets, but the difference was only significant on a normal salt diet, 165 +/- 15 versus 86 +/- 12 microGU/ml respectively. In animals with severe hydronephrosis the plasma renin levels were lower, and the changes less, than in those with mild and moderate hydronephrosis. CONCLUSION: This study demonstrates the presence of a salt-sensitive hypertension in hydronephrosis. A systemic effect of the renin-angiotensin system alone cannot be responsible for the hypertension.

Animals↗
PubMed2005

Influence of the adenosine A1 receptor on blood pressure regulation and renin release.

The present study was performed to investigate the role of adenosine A1 receptors in regulating blood pressure in conscious mice. Adenosine A1-receptor knockout (A1R-/-) mice and their wild-type (A1R+/+) littermates were placed on standardized normal-salt (NS), high-salt (HS), or salt-deficient (SD) diets for a minimum of 10 days before telemetric blood pressure and urinary excretion measurements in metabolic cages. On the NS diet, daytime and nighttime mean arterial blood pressure (MAP) was 7-10 mmHg higher in A1R-/- than in A1R+/+ mice. HS diet did not affect the MAP in A1R-/- mice, but the daytime and nighttime MAP of the A1R+/+ mice increased by approximately 10 mmHg, to the same level as that in the A1R-/-. On the SD diet, day- and nighttime MAP decreased by approximately 6 mmHg in both A1R-/- and A1R+/+ mice, although the MAP remained higher in A1R-/- than in A1R+/+ mice. Although plasma renin levels decreased with increased salt intake in both genotypes, the A1R-/- mice had an approximately twofold higher plasma renin concentration on all diets compared with A1R+/+ mice. Sodium excretion was elevated in the A1R-/- compared with the A1R+/+ mice on the NS diet. There was no difference in sodium excretion between the two genotypes on the HS diet. Even on the SD diet, A1R-/- mice had an increased sodium excretion compared with A1R+/+ mice. An abolished tubuloglomerular feedback response and reduced tubular reabsorption can account for the elevated salt excretion found in A1R-/- animals. The elevated plasma renin concentrations found in the A1R-/- mice could also result in increased blood pressure. Our results confirm that adenosine, acting through the adenosine A1 receptor, plays an important role in regulating blood pressure, renin release, and sodium excretion.

Animals↗
PubMed2005

Simultaneous changes of cell volume and cytosolic calcium concentration in macula densa cells caused by alterations of luminal NaCl concentration.

Cell volume and cytosolic Ca(2+) concentration ([Ca(2+)](i)) were measured in rabbit macula densa (MD) cells loaded with calcein and Fura Red using confocal microscopy. [Ca(2+)](i) was also analysed with Indo-1 and fura-2. We used isolated microperfused thick ascending limbs with attached glomerulus. The results showed that when the luminal NaCl concentration ('NaCl') was decreased from 35 to 10 mM, the cell volume decreased by 10.4%, and [Ca(2+)](i) increased by 9.5%. This increase was inhibited in Ca(2+)-free solution. When luminal [NaCl] was changed from 35 to 135 mM, the cell volume increased by 15.1%, and [Ca(2+)](i) did not change. The cell volume alterations were not different in Ca(2+)-free solutions. Using Indo-1, basal [Ca(2+)](i) in MD cells was 107.8 nM. When luminal [NaCl] was changed from 135 to 10 mm, [Ca(2)](i) increased by 23.5 nM. Using fura-2, the basal [Ca(2+)](i) in MD cells was 115.3 nM, and when luminal [NaCl] was changed from 135 or 35 to 10 mM, [Ca(2+)](i) change was 30.1 or 10.6 nM, respectively. An increase in [NaCl] caused no change in [Ca(2+)](i). In Ca(2+)-free solution, no change in [Ca(2+)](i) occurred. A stepwise decrease in luminal [NaCl] resulted in a sigmoid increase in [Ca(2+)](i) in MD cells. The steepest part of the curve was between 70 and 10 mM. In conclusion, we found that MD cells have cell volume regulation, and that [Ca(2+)](i) elevation caused by decreased luminal [NaCl] is independent of the cell volume.

Acid-Base Equilibrium↗
PubMed2005

Increased shear stress-released NO and decreased endothelial calcium in rat isolated perfused juxtamedullary nephrons.

BACKGROUND: Nitric oxide is an important vasodilator released from endothelial cells by the calcium-dependent endothelial nitric oxide synthase (NOS). We considered it important to investigate how shear stress/perfusion pressure influenced endothelial cell calcium concentration, nitric oxide release, and autoregulation of the afferent arteriole, since this arteriole controls glomerular filtration rate (GFR) and renin release. METHODS: We used an isolated perfused juxtamedullary nephron preparation and measured calcium with Fura 2, nitric oxide with 4-amino-5 methylamino-2', 7'-difluorescein (DAF-FM) and diameter with an imaging system. A mathematical model was applied to calculate changes in nitric oxide concentration and shear stress/wall tension during perfusion with and without erythrocytes at perfusion pressures varying from 50 to 150 mm Hg. RESULT: Cell-free perfusion increased nitric oxide concentration and abolished autoregulation; addition of erythrocytes or l-arginine analog N-nitro-l-arginine methyl ester (L-NAME) decreased nitric oxide concentration and reinstated autoregulation. Elevated perfusion pressure/elevated shear stress increased nitric oxide release and surprisingly decreased the endothelial cell calcium concentration, with perfusion pressure increase from 50 to 150 mm Hg, using blood perfusion endothelial calcium concentration decreased from 186 +/- 39 to 76 +/- 25 nmol/L and with cell-free perfusion from 116 +/- 33 to 56 +/- 21 nmol/L. CONCLUSION: Nitric oxide scavenging by erythrocytes has a high impact on arteriolar nitric oxide concentration and autoregulatory response. Nitric oxide measurements in endothelial cells of the afferent arteriole showed that increased perfusion pressure/shear stress increased nitric oxide release, while simultaneously endothelial cell calcium concentration decreased, possibly indicating a feedback control of this calcium by nitric oxide release.

Animals↗
PubMed2004

Hand-assisted retroperitoneoscopic live donor nephrectomy in comparison to open and laparoscopic procedures: a prospective study on donor morbidity and kidney function.

BACKGROUND: Living donor nephrectomy (LDN) is a unique surgical challenge where surgery is performed on a healthy individual. A new hand-assisted retroperitoneoscopic nephrectomy (HARS) technique was compared to transperitoneal laparoscopic nephrectomy (LAP) and open nephrectomy (OPEN). The aim was to examine the perioperative and postoperative morbidity, and the effects of the different surgical techniques with regard to renal function. METHODS: Donors (n=36) were divided into three groups (HARS, LAP and OPEN) according to surgical technique. During the operations, renal function, hormone output, warm ischemia time (WIT) and operating time were recorded. Renal function, complications, convalescence and allograft outcome were followed postoperatively for one year. RESULTS: OPEN and HARS groups showed similar operation times: 150 (95-218) minutes and 145 (124-225) minutes, respectively. LAP procedures took longer: 218 (163-280) minutes. OPEN had the shortest WIT at 91 (55-315) seconds; LAP had the longest WIT at 207 (100-319) seconds, with HARS at 180 (85-240) seconds. In all groups, glomerular filtration rate and urine production were decreased during surgery. Endoscopic techniques had a higher catecholamine release, and OPEN donors showed higher serum aldosterone. Endoscopic techniques showed shorter convalescence and less postoperative pain compared to OPEN. HARS had a smaller rise in creatinine than LAP, and HARS recipients a better creatinine clearance than the other groups in the early posttransplantation period. CONCLUSIONS: Evaluation of HARS shows that the operation is quick, the donors experience little pain, and recovery time is short. The renal function for donors and recipients is somewhat favorable to open surgery and transperitoneal laparoscopic approaches.

Adult↗
PubMed2004

Angiotensin II stimulates calcium and nitric oxide release from Macula densa cells through AT1 receptors.

A fluorescent nitric oxide (NO) indicator, 4,5-diaminofluorescein diacetate, and the calcium indicator, indo-1, with 488 nm and 364 nm UV confocal laser scanning microscopy were used to detect NO and calcium concentration in rabbit macula densa (MD) cells challenged by angiotensin II (Ang II). Glomeruli with attached thick ascending limbs with the MD plaque were isolated and perfused. Ang II concentration from 10(-9) to 10(-5) progressively increased MD cell calcium and NO to peak values at 10(-6) and 10(-7), respectively. Ang II (10(-6) M) caused the cytosolic calcium concentration ([Ca(2+)](i)) to increase by 125.8+/-16.3 nM (n=17) from the bath and by 52.3+/-11.5 nM (n=18) from the lumen. AT(1) antagonist CV-11974 (10(-6) M) blocked the Ang II-induced calcium responses from bath and lumen, but AT(2) antagonist PD-123319 (10(-6) M) did not. AT(2) agonist CGP-42112A (10(-6) M) did not affect [Ca(2+)](i) in MD cells from either side. Ang II (10(-6) M) increased the NO production by 16%+/-3.4% (n=26) from the bath and by 18%+/-3.1% (n=24) from the lumen. CV-11974 (10(-6) M) blocked the NO responses from both sides, but PD-123319 (10(-6) M) did not on either side. CGP-42112A (10(-6) M) had no effect on NO in MD cells. In calcium-free experiments there was no difference from the result in normal calcium solutions. In conclusion, we found that Ang II increased [Ca(2+)](i) and stimulated NO production in MD cells from the basolateral and luminal sides through AT(1) receptors.

Angiotensin II↗
PubMed2004

Neuronal nitric oxide synthase inhibition sensitizes the tubuloglomerular feedback mechanism after volume expansion.

BACKGROUND: In the kidney the neuronal isoform of nitric oxide synthase (nNOS) is located in the macula densa cells. These cells are known to be the sensor in the tubuloglomerular feedback. During volume expansion (VE), the tubuloglomerular feedback response is attenuated, allowing increased water and salt excretion. This study addressed the question whether inhibition of nNOS reestablishes the tubuloglomerular feedback response caused by acute extracellular VE. METHODS: In rats, VE was achieved by infusion of isotonic saline solution at 50 mL/hour x kg body weight. When urine flow was stabilized, the tubuloglomerular feedback response was evaluated by measuring changes in proximal tubular stop-flow pressure (PSF) in response to various loop of Henle perfusion rates. The loop of Henle was perfused with artificial ultrafiltrate and with addition of 1 mol/L non-specific NOS inhibitor, Nomega-nitro-l-arginine methyl ester (L-NAME). In additional rats the nNOS inhibitor, 7-nitro indazole (7-NI), was given intraperitoneally. Single nephron glomerular filtration rate (SNGFR) was also measured. GFR was determined after VE and nNOS inhibition. RESULTS: Acute VE decreased DeltaP(SF) and DeltaSNGFR while increasing the turning point, indicating decreased sensitivity of tubuloglomerular feedback response. After administration of L-NAME or 7-NI, DeltaP(SF) was maximally sensitized and the turning point and DeltaSNGFR were restored. GFR decreased after VE and nNOS inhibition compared to that after VE alone. CONCLUSION: These results suggest that a functioning nitric oxide system, especially through the nNOS, is important in mediating normal renal responses and that increased production of and/or sensitivity to nitric oxide during sustained VE plays an important role in the adaptive mechanism of the tubuloglomerular feedback.

Animals↗
PubMed2004

AT1 receptors mediate angiotensin II-induced release of nitric oxide in afferent arterioles.

BACKGROUND: Recent studies have indicated that angiotensin II (Ang II) possibly activates the nitric oxide (NO) system. We investigated the role of AT receptor subtypes (AT-R) in mediating the Ang II-induced NO release in afferent arterioles (Af) of mice. METHODS: Isolated Af of mice were perfused, and the isotonic contraction measured. Further, NO release was determined using DAF-FM, a fluorescence indicator for NO. Moreover, we qualitatively assessed the expression of AT-R at the mRNA level using reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Ang II reduced luminal diameters dose dependently (67.3 +/- 6.3% at 10(-6) mol/L). Inhibition of AT2-R with PD123.319 did not change the Ang II contractile response. AT1-R blockade with ZD7155 inhibited contraction. Stimulation of AT2-R during AT1-R inhibition with ZD7155, and preconstriction with norepinephrine (NE) had no influence on the diameter. Drug application via the perfusion pipette changed flow and pressure, and enhanced NO fluorescence by DeltaF = 4.0 +/- 0.4% (N= 14, background). Luminal application of Ang II (10(-7) mol/L) increased the NO fluorescence by DeltaF = 9.9 +/- 1.2% (N= 8). AT1-R blockade blunted the increase to background levels (DeltaF to 4.0 +/- 0.3%, N= 6, P < 0.05), but AT2-R blockade did not (8.1 +/- 0.9%, N= 9). L-NAME nearly abolished the Ang II effect on the NO fluorescence (DeltaF = 1.6 +/- 0.5% (N= 8). NE did not increase NO release beyond the background levels. RT-PCR showed expression of both AT1-R and AT2-R. CONCLUSION: The results indicate an Ang II-induced NO release in Af of mice, which is mediated by AT1-R. Thus, Ang II balances its own constrictor action in Af. This control mechanism is very important in view of high renin and angiotensin II concentration in the juxtaglomerular apparatus.

Angiotensin II↗
PubMed2004

Distal renal tubular acidosis in mice that lack the forkhead transcription factor Foxi1.

While macro- and microscopic kidney development appear to proceed normally in mice that lack Foxi1, electron microscopy reveals an altered ultrastructure of cells lining the distal nephron. Northern blot analyses, cRNA in situ hybridizations, and immunohistochemistry demonstrate a complete loss of expression of several anion transporters, proton pumps, and anion exchange proteins expressed by intercalated cells of the collecting ducts, many of which have been implicated in hereditary forms of distal renal tubular acidosis (dRTA). In Foxi1-null mutants the normal epithelium with its two major cell types - principal and intercalated cells - has been replaced by a single cell type positive for both principal and intercalated cell markers. To test the functional consequences of these alterations, Foxi1(-/-) mice were compared with WT littermates in their response to an acidic load. This revealed an inability to acidify the urine as well as a lowered systemic buffer capacity and overt acidosis in null mutants. Thus, Foxi1(-/-) mice seem to develop dRTA due to altered cellular composition of the distal nephron epithelium, thereby denying this epithelium the proper gene expression pattern needed for maintaining adequate acid-base homeostasis.

Acidosis, Renal Tubular↗
PubMed2003

Effects of increased intra-abdominal pressure and volume expansion on renal function in the rat.

BACKGROUND: The effects of increased intra-abdominal pressure (IAP) and volume expansion on renal function in the rat were studied to gain more knowledge of the oliguria seen during laparoscopic procedures and to reduce the detrimental renal effects of IAP. METHODS: IAP was elevated to 5 or 10 mmHg by insufflation of CO(2) and maintained for 2 h in anaesthetized and mechanically ventilated rats. Rats with normal IAP served as controls. An angiotensin II receptor I antagonist, candesartan, was given as a bolus injection and a 5% volume expansion was achieved by i.v. saline infusion. An angiotensin-converting enzyme (ACE) inhibitor was also given. Renal parameters were the glomerular filtration rate (GFR), urine production, the urinary concentrations of sodium and potassium and the osmolality in the urine. The arterial acid-base balance and blood pressure were also monitored. RESULTS: The GFR deteriorated by 70% during pneumoperitoneum (PP) of 10 mmHg. There was a dramatic drop in sodium excretion (88-97%). With candesartan and elevated IAP, there was a drop in mean arterial pressure (from 90 to 55 mmHg) and the negative renal effects were very pronounced. Renal function was better preserved during elevated IAP in combination with volume expansion. CONCLUSIONS: Capnoperitoneum suppresses renal function, especially in combination with angiotensin II receptor 1 blockade and ACE inhibition. Volume expansion reduces the deleterious effects of PP on renal function during elevated IAP. The results suggest that patients should not be given pharmaceuticals blocking the renin-angiotensin-aldosterone system prior to procedures that may increase IAP. It may be beneficial, however, to reduce angiotensin II tension by volume expansion.

Angiotensin II Type 1 Receptor Blockers↗
PubMed2002

Macula densa neuronal nitric oxide synthase.

In the juxtaglomerular apparatus of the kidney the distal tubule returns to its own glomerulus where specialised cells, the macula densa (MD) cells, are located so that they come in contact with the tubular fluid. It is well documented that MD cells sense the distal tubular flow-rate and that when the flow is too high they are activated, which leads to vasoconstriction of the afferent arteriolar, the tubuloglomerular feedback (TGF). Neuronal nitric oxide synthase (nNOS) is largely expressed in the MD cells. Acute inhibition of MD nNOS leads to an enhanced TGF response, indicating that nitric oxide (NO) is an important short-term modulator for volume regulation in the body. By contrast, the NO from the nNOS of the MD cells does not seem to play a role in the long-term adaptations of renin release in low- or high-salt diets.

Animals↗
PubMed2002

Purinergic receptor signaling at the basolateral membrane of macula densa cells.

Purinergic receptors are important in the regulation of renal hemodynamics; therefore, this study sought to determine if such receptors influence macula densa cell function. Isolated glomeruli containing macula densa cells, with and without the cortical thick ascending limb, were loaded with the Ca(2+) sensitive indicators, Fura Red (confocal microscopy) or fura 2 (conventional video image analysis). Studies were performed on an inverted microscope in a chamber with a flow-through perfusion system. Changes in cytosolic calcium concentration ([Ca(2+)](i)) from exposed macula densa plaques were assessed upon addition of adenosine, ATP, UTP, ADP, or 2-methylthio-ATP (2- MeS-ATP) for 2 min added to the bathing solution. There was no change in [Ca(2+)](i) with addition of adenosine (10(-7) to 10(-3) M). UTP and ATP (10(-4) M) caused [Ca(2+)](i) to increase by 268 +/- 40 nM (n = 21) and 295 +/- 53 nM (n = 21), respectively, whereas in response to 2MesATP and ADP, [Ca(2+)](i) increased by only 67 +/- 13 nM (n = 8) and 93 +/- 36 nM (n = 14), respectively. Dose response curve for ATP (10(-7) to 10(-3) M) added in bath showed an EC(50) of 15 microM. No effect on macula densa [Ca(2+)](i) was seen when ATP was added from the lumen. ATP caused similar increases in macula densa [Ca(2+)](i) in the presence or absence of bath Ca(2+) and addition of 5 mM ethyleneglycotetraacetic acid (EGTA). Suramin (an antagonist of P2X and P2Y receptors) completely inhibited ATP-induced [Ca(2+)](i) dynamics. Also, ATP-Ca(2+) responsiveness was prevented by the phospholipase C inhibitor, U-73122, but not by its inactive analog, U-73343. These results suggest that macula densa cells possess P2Y(2) purinergic receptors on basolateral but not apical membranes and that activation of these receptors results in the mobilization of Ca(2+).

Adenosine Diphosphate↗
PubMed2002

Changes of cell volume and nitric oxide concentration in macula densa cells caused by changes in luminal NaCl concentration.

The luminal NaCl concentration ([NaCl]) at the macula densa (MD) controls both tubuloglomerular feedback (TGF) and renin release. Nitric oxide (NO) inhibits TGF sensitivity to a great extent. The NO concentration in the MD cells is not known. This study measured this concentration in MD cells with confocal microscopy in the isolated perfused thick ascending limb using a NO-sensitive fluorophore 4,5-diaminofluorescein (DAF-2). Calcein was used to measure cell volume changes. The loop perfusion fluid was a modified Ringer solution containing 10, 35, or 135 mM NaCl with a constant total osmolarity (290 mOsm), and the bath was perfused with the 135 mM NaCl solution. The results show that MD cell volume and NO concentration measured with DAF-2 DA increased considerably with increasing luminal [NaCl] and with calcium-free solutions in the lumen and bath. L-arginine (5 mM) increased NO concentration in the MD cells by 30%. 7-nitroindazole could totally inhibit the NO production caused by L-arginine and by increased luminal [NaCl]. In conclusion, the MD cell volume changes caused by the changes of luminal [NaCl] were quantitatively measured, and it was found that increasing the luminal [NaCl] resulted in an increase in cell volume. It was also found that NO formation in MD cells could be measured with DAF-2 and that NO production was increased through neuronal NO synthase activation with an increased luminal [NaCl]. An increased NO production will inhibit the vasoconstriction induced by the TGF and at the same time will reduce TGF sensitivity.

Animals↗
PubMed2002

Nitric oxide induces resensitization of P2Y nucleotide receptors in cultured rat mesangial cells.

Receptor desensitization of G protein-coupled receptors (GPCRs), which occurs during short-term (seconds to minutes) exposure of cells to agonists, is mediated by phosphorylation and receptor endocytosis. Recycling of the receptors is a requisite for resensitization of the response. The mechanisms that attenuate signaling by GPCRs are of considerable importance to regulation of intercellular signaling and maintenance of their ability to respond to agonists over time. This study evaluates the effect of nitric oxide (NO) on P2Y nucleotide receptor resensitization in cultured rat glomerular mesangial cells. The NO production in cultured mesangial cells was measured by using confocal microscopy and the fluorescence NO indicator 4,5-diaminofluorescein diacetate (DAF-2 DA). L-arginine increased and Nomega-nitro-L-arginine methyl ester (L-NAME) decreased NO production significantly (P < 0.05). Calcium responses to ATP were measured with fura-2 and imaging techniques. Repeated stimulation with ATP results in receptor desensitization that is characterized by lower calcium peak amplitude. Desensitization was induced by challenging mesangial cells with four consecutive 2-min pulses of ATP (0.1 mM) separated by 4.5-min control perfusions. Intracellular calcium concentration ([Ca2+]i) increase evoked by second, third, and fourth ATP challenges were about 40%, 26%, and 18% of the first one. The NO precursor, L-arginine (10 mM), and the NO donors, spermine-NONOate (500 microM) and sodium nitroprusside (SNP) (1 mM), were added before and during a fourth ATP challenge. Spermine-NONOate and L-arginine induced a recovery of the [Ca2+]i response to the fourth ATP challenge (P < 0.01 and 0.05, respectively). The NO synthase inhibitor, L-NAME (5 mM), applied along with ATP, was shown to enhance desensitization. 1H-(1,2,4)oxadiazolo(4,3-alpha)quinoxalin-1-one (ODQ, 30 microM), an inhibitor of guanylate cyclase, was used along with L-arginine, SNP, or spermine-NONOate. There was no significant difference with or without ODQ. Neither ODQ nor 8-Br-cGMP, an analog of cGMP, at different concentrations showed effects on ATP-stimulated [Ca2+]i. There was no elevation of [Ca2+]i when the cells were challenged by different concentrations (1 microM, 100 microM, 1 mM, 20 mM, and 30 mM) of caffeine, caffeine plus ATP (0.1 mM), and 4-chloro-3-ethylphenol (100 microM, 500 microM, and 1 mM), a new agonist of ryanodine receptors. The results indicate that NO can increase the P2Y receptor resensitization in rat glomerular mesangial cells by acting through a cGMP-independent pathway. No evidence was found for the existence of ryanodine-sensitive intracellular calcium stores in rat mesangial cells.

Animals↗