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Biomedical subjects

Edward W Inscho

Publications and source records attributed to Edward W Inscho.

At least 19 recordsLinked to original sources
PubMed2007

Attenuated vasoconstrictor responses to endothelin in afferent arterioles during a high-salt diet.

Endothelin-1 (ET-1) is increased in rats on a high-salt (HS) diet and participates in salt-dependent hypertension. Afferent arterioles (AA) are important for long-term blood pressure control, and therefore we hypothesized that a HS diet would alter their responsiveness to ET-1. Sprague-Dawley rats were fed either a normal-salt (NS; 0.66% NaCl) or HS (8%) diet for 1 wk. Diameters of AA were determined in response to increasing concentrations of big ET-1, ET-1, sarafotoxin 6c (S6c), or norepinephrine (NE), using the blood-perfused juxtamedullary nephron technique. ET-1 responses were also determined during blockade of endothelin type A (ET(A)) or type B (ET(B)) receptors with 10 nM ABT-627 or 30 nM A-192621, respectively. Expression of ET(A) and ET(B) receptors was determined in renal microvessels. Responses of AA to big ET-1, ET-1, and S6c were significantly attenuated during a HS diet (e.g., response to 10(-10) M ET-1 in NS vs. HS rats: -52.5 +/- 10.2 vs. +5.6 +/- 11.3% of control diameter; P < 0.05), with no change in the responses to NE. ET(B), but not ET(A) receptor blockade abolished the different response to ET-1 between the NS and HS groups. ET(B) receptor expression in renal microvessels was increased in response to HS (17.7 +/- 2.4 vs. 6.6 +/- 3.0% of beta-actin, P = 0.02), whereas ET(A) receptor expression was unchanged. These results suggest that the reduced vasoconstrictor response of AA to endothelin peptides during a HS diet is mediated by increased vasodilatory function of endothelial ET(B) receptors. By preserving renal blood flow, this may be an important mechanism to restore sodium balance during a HS diet.

Animals↗
PubMed2007

P2 receptor regulation of [Ca2+]i in cultured mouse mesangial cells.

Experiments were performed to establish the pharmacological profile of purinoceptors and to identify the signal transduction pathways responsible for increases in intracellular calcium concentration ([Ca(2+)](i)) for cultured mouse mesangial cells. Mouse mesangial cells were loaded with fura 2 and examined using fluorescent spectrophotometry. Basal [Ca(2+)](i) averaged 102 +/- 2 nM (n = 346). One hundred micromolar concentrations of ATP, ADP, 2',3'-(benzoyl-4-benzoyl)-ATP (BzATP), ATP-gamma-S, and UTP in normal Ca(2+) medium evoked peak increases in [Ca(2+)](i) of 866 +/- 111, 236 +/- 18, 316 +/- 26, 427 +/- 37, and 808 +/- 73 nM, respectively. UDP or 2-methylthio-ATP (2MeSATP) failed to elicit significant increases in [Ca(2+)](i), whereas identical concentrations of adenosine, AMP, and alpha,beta-methylene ATP (alpha,beta-MeATP) had no detectable effect on [Ca(2+)](i). Removal of Ca(2+) from the extracellular medium had no significant effect on the peak increase in [Ca(2+)](i) induced by ATP, ADP, BzATP, ATP-gamma-S, or UTP compared with normal Ca(2+); however, Ca(2+)-free conditions did accelerate the rate of decline in [Ca(2+)](i) in cells treated with ATP and UTP. [Ca(2+)](i) was unaffected by membrane depolarization with 143 mM KCl. Western blot analysis for P2 receptors revealed expression of P2X(2), P2X(4), P2X(7), P2Y(2), and P2Y(4) receptors. No evidence of P2X(1) and P2X(3) receptor expression was detected, whereas RT-PCR analysis reveals mRNA expression for P2X(1), P2X(2), P2X(3), P2X(4), P2X(7), P2Y(2), and P2Y(4) receptors. These data indicate that receptor-specific P2 receptor activation increases [Ca(2+)](i) by stimulating calcium influx from the extracellular medium and through mobilization of Ca(2+) from intracellular stores in cultured mouse mesangial cells.

Animals↗
PubMed2005

Impaired Ca2+ signaling attenuates P2X receptor-mediated vasoconstriction of afferent arterioles in angiotensin II hypertension.

This study tested the hypothesis that afferent arteriolar responses to purinoceptor activation are attenuated, and Ca2+ signaling mechanisms are responsible for the blunted preglomerular vascular reactivity in angiotensin II (Ang II) hypertension. Experiments determined the effects of ATP, the P2X1 agonist beta,gamma-methylene ATP or the P2Y agonist UTP on arteriolar diameter using the juxtamedullary nephron technique and on renal myocyte intracellular Ca2+ concentration ([Ca2+]i) using single cell fluorescence microscopy. Six or 13 days of Ang II infusion significantly attenuated the vasoconstrictor responses to ATP and beta,gamma-methylene ATP (P<0.05). During exposure to ATP (1, 10, and 100 micromol/L), afferent diameter declined by 17+/-2%, 29+/-3%, and 30+/-2% in normal control rats and 8+/-3%, 7+/-3%, and 22+/-3% in kidneys of Ang II-infused rats (13 days). Renal myocyte intracellular calcium responses to ATP or beta,gamma-methylene ATP were also decreased in Ang II hypertensive rats. In myocytes of control rats, peak increases in [Ca2+]i averaged 107+/-21, 170+/-38, and 478+/-79 nmol/L at ATP concentrations of 1, 10, and 100 micromol/L, respectively. Ang II infusion for 13 days decreased the peak responses to ATP (1, 10, and 100 micromol/L) to 65+/-13, 102+/-20, and 367+/-73 nmol/L, respectively. The peak increases in [Ca2+]i in response to beta,gamma-methylene ATP were also reduced in Ang II hypertensive rats. However, angiotensin hypertension did not change the UTP-mediated vasoconstrictor responses or the myocyte calcium responses to UTP. These results indicate that the impaired autoregulatory response observed in Ang II-dependent hypertension can be attributed to impairment of P2X1 receptor-mediated signal transduction.

Adenosine↗
PubMed2005

Calcium and chloride channel activation by angiotensin II-AT1 receptors in preglomerular vascular smooth muscle cells.

The pathways responsible for the rapid and sustained increases in [Ca(2+)](i) following activation of ANG II receptors (AT(1)) in renal vascular smooth muscle cells were evaluated using fluorescence microscopy. Resting intracellular calcium concentration [Ca(2+)](i) averaged 75 +/- 9 nM. The response to ANG II (100 nM) was characterized by a rapid initial increase of [Ca(2+)](i) by 74 +/- 6 nM (n = 35) followed by a decrease to a sustained level of 12 +/- 2 nM above baseline. The average time from peak to 50% reduction from the peak value (50% time point) was 32 +/- 4 s. AT(1) receptor blockade with 1 microM candesartan (n = 5) prevented the responses to ANG II. In nominally calcium-free conditions (n = 8), the peak increase in [Ca(2+)](i) averaged 42 +/- 7 nM but the sustained phase was absent and the 50% time point was reduced to 11 +/- 4 s. L-type calcium channel blockade with diltiazem reduced the peak [Ca(2+)](i) to 24 +/- 8 nM and the sustained level to 4 +/- 2 nM (n = 10). In cells preincubated in low Cl(-) (3.0 mM), the peak response to ANG II was suppressed as was the sustained response. Blockade of chloride channels with DIDS eliminated both the peak and sustained responses (n = 11); chloride channel blockade with DPC (n = 17) suppressed the peak increase in [Ca(2+)](i) to 18 +/- 5 and also prevented the sustained response. IP3 receptor blockade by 10 microM TMB-8 (n = 6) reduced the peak to 22 +/- 8 and prevented the sustained response. Exposure to 10 microM TMB-8 in the presence of Ca(2+)-free medium prevented the ANG II response (n = 9). In the presence of 100 microM DPC and 10 microM TMB-8 (n = 7), the ANG II response was also prevented. Thus the rapid initial increase in [Ca(2+)](i) is due not only to release from intracellular stores, but also to Ca(2+) influx from the extracellular fluid. Although Ca(2+) entry via L-type calcium channels is responsible for the major portion of the sustained response, other entry pathways participate. The finding that chloride channel blockers markedly attenuate both rapid and sustained responses indicates that chloride channel activation contributes to, rather than being the consequence of, the initial rapid response.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2005

TGF-beta impairs renal autoregulation via generation of ROS.

Impaired autoregulation in chronic kidney disease can result in elevation of glomerular capillary pressure and progressive glomerular damage; however, the factors linking chronic glomerular disorders to impaired autoregulation have not been identified. We tested the hypothesis that the cytokine most closely associated with progressive glomerular disease, transforming growth factor (TGF)-beta, may also attenuate autoregulation. Kidneys from normal rats were prepared for videomicroscopy, using the blood-perfused juxtamedullary nephron technique. Autoregulatory responses were measured under control conditions and during superfusion with TGF-beta1 (10 ng/ml). Control afferent arteriolar diameter averaged 18.4 +/- 1 microm and significantly decreased to 16.3 +/- 0.9 and 13.2 +/- 0.8 microm at perfusion pressures of 130 and 160 mmHg, respectively. In the presence of TGF-beta1, autoregulatory responses were completely blocked. In similar experiments performed using PDGF-BB (10 ng/ml) and HGF (25 ng/ml), the normal autoregulatory response was not affected. In vitro studies, using isolated preglomerular vascular smooth muscle cells, revealed that exposure to TGF-beta1 stimulated a rapid increase in reactive oxygen species (ROS) that was inhibited by NADPH oxidase inhibitors. In situ studies, with dihydroethidium staining, revealed a marked increase in renal vessel ROS production on exposure to TGF-beta1. Pretreatment of the juxtamedullary afferent arterioles with tempol, a ROS scavenger, or with apocynin, a NADPH oxidase inhibitor, prevented the impaired autoregulation induced by TGF-beta1. These data reveal a novel hemodynamic pathway by which TGF-beta could lead to progressive glomerular injury by impairing normal renal microvascular function.

Animals↗
PubMed2005

ETA and ETB receptors differentially modulate afferent and efferent arteriolar responses to endothelin.

The segment-specific actions of endothelin peptides and agonists have not been thoroughly investigated in the renal microcirculation. The current studies were performed to assess the relative contribution of ET(A) and ET(B) receptors to the renal pre- and postglomerular arteriolar responses to ET-1. Experiments determined the effect of selective ET(A) (A-127722; 30 nM) and ET(B) (A-192621; 30 nM) receptor blockade, on arteriolar responses to ET-1 concentrations of 1 pM to 10 nM in rat kidneys using the isolated juxtamedullary nephron technique. Renal perfusion pressure was set at 110 mmHg. Baseline afferent arteriolar diameter was similar in all groups and averaged 17.8+/-0.6 microm (n=14). In control experiments (n=6), ET-1 produced significant concentration-dependent decreases in arteriolar diameter, with 10 nM ET-1 decreasing diameter by 85+/-1%. Selective blockade of ET(A) receptors (n=6) prevented ET-1-mediated vasoconstriction, except at concentrations of 1 and 10 nM. Similarly, the vasoconstrictor profile was right shifted during selective ET(B) receptor blockade (n=4). Combined ET(A) and ET(B) receptor blockade (n=5) completely abolished afferent arteriolar diameter responses to ET-1. ET(B) selective agonists (S6c and IRL-1620) produced disparate responses. S6c produced a concentration-dependent vasoconstriction of afferent arterioles. In contrast, S6c produced a concentration-dependent dilation of efferent arterioles that could be blocked with an ET(B) receptor antagonist. IRL-1620, another ET(B) agonist, was less effective at altering afferent or efferent diameter and produced a small reduction in pre- and postglomerular arteriolar diameter. These data demonstrate that both ET(A) and ET(B) receptors participate in ET-1-mediated vasoconstriction of afferent arterioles. ET(B) receptor stimulation provides a significant vasodilatory influence on the efferent arteriole. Furthermore, since selective ET(A) and ET(B) receptor antagonists abolished preglomerular vasoconstrictor responses at lower ET-1 concentrations, these data support a possible interaction between ET(A) and ET(B) receptors in the control of afferent arteriolar diameter.

Animals↗
PubMed2004

L-type calcium channels in the renal microcirculatory response to endothelin.

The signaling pathways of endothelin (ET)-1-mediated vasoconstriction in the renal circulation have not been elucidated but appear to be distinct between ET(A) and ET(B) receptors. The purpose of this study was to determine the role of L-type Ca(2+) channels in the vasoconstrictor response to ET-1 and the ET(B) receptor agonist sarafotoxin 6c (S6c) in the rat kidney. Renal blood flow (RBF) was measured with an ultrasonic flow probe in anesthetized rats, and a microcatheter was inserted into the renal artery for drug infusion. All rats were given vehicle (0.9% NaCl) or three successive bolus injections (1, 10, and 100 pmol) of ET-1 or S6c at 30-min intervals (n = 6 in each group). ET-1 and S6c produced dose-dependent decreases in RBF. The Ca(2+) channel blocker nifedipine (1.5 mug) significantly attenuated the RBF response only at the highest doses of ET-1 and S6c. In the isolated blood-perfused juxtamedullary nephron preparation, Ca(2+) channel blockade with diltiazem had a very small inhibitory effect on ET-1-induced decreases in afferent arteriolar diameter only at the lowest concentrations of ET-1. In vascular smooth muscle cells isolated from preglomerular vessels, ET-1 produced a typical biphasic Ca(2+) response, whereas S6c had no effect on cytosolic Ca(2+). Furthermore, Ca(2+) channel blockade (diltiazem or Ni(2+)) had no effect on the peak or sustained increase in cytosolic Ca(2+) produced by ET-1. These results support the hypothesis that L-type Ca(2+) channels play only a minor role in the constrictor responses to ET-1 in the renal microcirculation.

Animals↗
PubMed2004

P2X receptor-stimulated calcium responses in preglomerular vascular smooth muscle cells involves 20-hydroxyeicosatetraenoic acid.

The current study tested the hypothesis that endogenous 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to the increase in intracellular calcium ([Ca2+]i) elicited by P2X receptor activation in renal microvascular smooth muscle cells. Vascular smooth muscle cells obtained from rats were loaded with fura-2 and studied using standard single cell fluorescence microscopy. Basal renal myocyte [Ca2+]i averaged 96 +/- 5 nM. ATP (10 and 100 microM) increased vascular smooth muscle cell [Ca2+]i by 340 +/- 88 and 555 +/- 80 nM, respectively. The cytochrome P450 hydroxylase inhibitor, N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), or the 20-HETE antagonist, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE), significantly attenuated the peak myocyte [Ca2+]i responses to 10 and 100 microM ATP. ATP (100 microM) increased vascular smooth muscle cell [Ca2+]i by 372 +/- 93 and 163 +/- 55 nM in the presence of DDMS or 20-HEDE, respectively. The P2X receptor agonist, alpha,beta-methylene-ATP (10 microM), increased myocyte [Ca2+]i by 78 +/- 12 nM, and this response was significantly attenuated by DDMS (40 +/- 15 nM). In contrast, the vascular smooth muscle cell [Ca2+]i evoked by the P2Y agonist, UTP (100 microM), was not altered by DDMS or 20-HEDE. The effect of 20-HETE on [Ca2+]i was also assessed, and the peak increases in [Ca2+]i averaged 62 +/- 12 and 146 +/- 70 nM at 20-HETE concentrations of 1 and 10 microM, respectively. These results demonstrate that 20-HETE plays a significant role in the renal microvascular smooth muscle cell [Ca2+]i response to P2X receptor activation.

Adenosine Triphosphate↗
PubMed2004

Age-related alterations in NOS and oxidative stress in mesenteric arteries from male and female rats.

Epidemiological evidence suggests that advancing age affects the cardiovascular system of men and women differently. The purpose of this study was to determine whether the effects of aging on nitric oxide synthase (NOS), oxidative stress, and vascular function are different in males and females. Mesenteric arteries from young (3 mo) and old (24 mo) male and female Fischer 344/Brown Norway rats were studied. Western blot analysis and NOS activity were performed on the homogenized mesenteric arterial bed separated into cytosolic and membrane-associated fractions. Plasma 8-isoprostane measurements assessed oxidative stress. Vascular reactivity was determined by using a wire myograph in the absence and presence of a NOS inhibitor, N(omega)-nitro-l-arginine, to examine endothelial function and basal and stimulated nitric oxide release. In additional arteries, reactivity was performed in the presence of polyethylene glycol-SOD to assess the impact of superoxide on vascular function. Among females, aging was associated with a decline in membrane-associated NOS activity and membrane-associated NOS III protein expression. Advancing age in males was associated with increased cytosolic NOS III protein expression. Among both males and females, advancing age resulted in increased oxidative stress. Vascular function was maintained with age in arteries from both males and females, and there was no difference in either basal or stimulated nitric oxide release with age. Despite sex-specific effects of advancing age on the NOS system and increases in markers of oxidative stress, vascular function is maintained in mesenteric arteries from aged Fischer 344/Brown Norway rats. These data suggest that age-related alterations in the resistance vasculature are complex and likely involve multiple compensating vasoactive pathways.

Aging↗
PubMed2004

Elevated arterial pressure impairs autoregulation independently of AT(1) receptor activation.

OBJECTIVE: These studies determined the ability of AT1 receptor blockade or 'triple therapy', to reverse angiotensin II-induced hypertension and improve autoregulatory behavior. DESIGN: Experiments to determine if regulation of systolic blood pressure, in the normotensive range, would improve renal microvascular autoregulatory behavior in angiotensin II-infused rats. METHODS: Hypertension was induced by chronic angiotensin II infusion (60 ng/min) for 10-14 days. Two groups of angiotensin II-infused rats received either AT1 receptor blockade, with candesartan cilexetil, or triple therapy, with hydralazine, hydrochlorothiazide and reserpine, beginning on day 6 or day 0 of angiotensin II infusion, respectively. Sham animals were studied as normotensive controls. Systolic blood pressure was measured by tail cuff. Autoregulatory behavior was assessed using the juxtamedullary nephron technique in response to step (15 mmHg) increases in perfusion pressure from 65 to 170 mmHg. RESULTS: Angiotensin II infusion increased systolic blood pressure from a baseline of 125 mmHg to 162 and 182 mmHg after 10 and 14 days, respectively. Candesartan cilexetil and triple therapy normalized the blood pressure to between 119 and 126 mmHg. Increasing perfusion pressure, from 65 to 170 mmHg, reduced afferent arteriolar diameter by 30% in sham-treated kidneys. Autoregulation was significantly blunted in angiotensin II-infused rats, resulting in a pressure-mediated vasoconstriction of only 10%. Candesartan cilexetil, or triple therapy, significantly improved autoregulatory behavior, as indicated by pressure-mediated vasoconstrictor responses of 30 and 40%; respectively, despite continued angiotensin II infusion. CONCLUSIONS: These data suggest that chronic elevation of arterial blood pressure, rather than chronic AT1 receptor stimulation, is sufficient to induce hypertensive impairment of renal autoregulatory capability.

Angiotensin II↗
PubMed2004

Role of interstitial ATP and adenosine in the regulation of renal hemodynamics and microvascular function.

The role of adenosine in the regulation of renal hemodynamics and function has been studied extensively; however, another purine agent, ATP, is also gaining recognition for its paracrine role in the kidney. Adenosine and ATP bind to specific membrane-bound P1 and P2 purinoceptors, respectively, and initiate a variety of biological effects on renal microvascular tone, mesangial cell function, and renal epithelial transport. The purpose of this review is to summarize the potential roles of interstitial ATP and adenosine as regulators of renal hemodynamics and microcirculation. In vitro blood-perfused juxtamedullary nephron preparation was used to assess the roles of ATP and adenosine in the regulation of renal microvascular tone. This approach mimics the adventitial exposure of renal microvascular smooth muscle to ATP and adenosine synthesized locally and released into the interstitial fluid. ATP selectively vasoconstricts afferent but not efferent arterioles via P2X and P2Y receptors, whereas, adenosine vasoconstricts both vascular segments via activation of adenosine A(1) receptors. Furthermore, selective P2X and P2Y receptor stimulation increases intracellular calcium concentration in vascular smooth muscle cells that are freshly isolated from the preglomerular microvasculature. These data support the hypothesis that interstitial ATP plays a critical role in the control of renal microvascular function through mechanisms that are independent of adenosine receptors. We have recently developed a renal microdialysis method to determine the dynamics of ATP and adenosine levels in the renal cortical interstitium. In this review, we also summarize current knowledge pertaining to the alterations in renal interstitial ATP and adenosine in some pathophysiological conditions.

Adenosine↗
PubMed2003

12-Hydroxyeicosatetraenoic acid participates in angiotensin II afferent arteriolar vasoconstriction by activating L-type calcium channels.

The lipoxygenase (LO) metabolite, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], constricts renal vessels, contributes to the vascular response to angiotensin, and has been implicated in cardiovascular and renal diseases. The current studies were performed to determine if renal microvascular 12(S)-HETE production is stimulated by angiotensin and the contribution of L-type calcium channels to the vasoconstriction elicited by 12(S)-HETE. Angiotensin increased renal microvascular 12(S)-HETE production by 64%, whereas cyclooxygenase metabolite production was not altered. Renal microvessels also expressed platelet-type 12-LO and leukocyte-type 12-LO. In the juxtamedullary preparation, afferent arteriolar diameter averaged 21 +/- 1 microm and 12(S)-HETE caused a graded decrease in vessel caliber. The afferent arteriolar response to 12(S)-HETE was abolished during L-type calcium channel inhibition. Renal microvascular smooth muscle cells were studied using fluorescence microscopy. Renal myocyte [Ca2+]i averaged 93 +/- 5 nmol/l. The 12(S)-HETE (5 micromol/l) increased myocyte [Ca2+]i to a peak value of 340 +/- 55 nmol/l. The peak [Ca2+]i response following exposure to 12(S)-HETE was greatly attenuated in the absence of extracellular Ca2+ or calcium channel blockade. These results demonstrate that renal microvascular 12(S)-HETE production is increased in response to angiotensin, and activation of L-type calcium channels is an important mechanism responsible for the afferent arteriolar vasoconstriction elicited by 12(S)-HETE.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed2003

Physiological role for P2X1 receptors in renal microvascular autoregulatory behavior.

This study tests the hypothesis that P2X1 receptors mediate pressure-induced afferent arteriolar autoregulatory responses. Afferent arterioles from rats and P2X1 KO mice were examined using the juxtamedullary nephron technique. Arteriolar diameter was measured in response to step increases in renal perfusion pressure (RPP). Autoregulatory adjustments in diameter were measured before and during P2X receptor blockade with NF279 or A1 receptor blockade with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). Acute papillectomy or furosemide perfusion was performed to interrupt distal tubular fluid flow past the macula densa, thus minimizing tubuloglomerular feedback-dependent influences on afferent arteriolar function. Under control conditions, arteriolar diameter decreased by 17% and 29% at RPP of 130 and 160 mmHg, respectively. Blockade of P2X1 receptors with NF279 blocked pressure-mediated vasoconstriction, reflecting an attenuated autoregulatory response. The A1 receptor blocker DPCPX did not alter autoregulatory behavior or the response to ATP. Deletion of P2X1 receptors in KO mice significantly blunted autoregulatory responses induced by an increase in RPP, and this response was not further impaired by papillectomy or furosemide. WT control mice exhibited typical RPP-dependent vasoconstriction that was significantly attenuated by papillectomy. These data provide compelling new evidence indicating that tubuloglomerular feedback signals are coupled to autoregulatory preglomerular vasoconstriction through ATP-mediated activation of P2X1 receptors.

Adenosine Triphosphate↗
PubMed2002

Decreased renal cytochrome P450 2C enzymes and impaired vasodilation are associated with angiotensin salt-sensitive hypertension.

Excess dietary salt intake differentially modulates the activity of cytochrome (CYP) P450 enzymes in kidney cortex. Exactly how increased angiotensin (Ang) II levels and hypertension change the regulatory effect of high salt on CYP450 enzymes remains unclear. The present study investigated the effects of combined administration of Ang II and a high-salt diet on P450 epoxygenase and hydroxylase protein levels in kidney, as well as afferent arteriolar responses to acetylcholine and sodium nitroprusside. High dietary salt administration for 14 days resulted in increased renal cortical CYP2C11 protein levels, and a significant increase of CYP2C11 and CYP2C23 protein levels in renal microvessels. Administration of Ang II in combination with a high-salt diet prevented the upregulation of renal cortical CYP2C11 protein expression observed with high dietary salt alone, and significantly downregulated expression of CYP2C11, CYP2C23, and CYP2J protein in renal microvessels. A high-salt diet alone decreased CYP4A protein in kidney cortex, and renal cortical CYP4A protein level remained at a low level in Ang II-infused rats treated with a high-salt diet. Increases in blood pressure during Ang II infusion were greater in rats fed a high-salt diet. In addition, afferent arteriolar responsiveness to acetylcholine and sodium nitroprusside was significantly attenuated in Ang II-treated rats versus controls. This decrease was significantly enhanced in Ang II-treated rats given a high-salt diet. These results support the hypothesis that an inability to upregulate CYP2C and maintain CYP2J in the rat kidney and impaired afferent arteriolar vasodilation with chronic Ang II infusion contribute to salt-induced elevation of arterial pressure.

Angiotensin II↗
PubMed2002

Modulation of intracellular calcium and calmodulin by melatonin in MCF-7 human breast cancer cells.

The pineal hormone, melatonin, has been shown to inhibit the proliferation of the estrogen receptor alpha (ERalpha)-positive macrophage chemotactic factor (MCF)-7 human breast cancer cells. Previous studies from other systems indicate that melatonin modulates the calcium (Ca2+)/calmodulin (CaM) signaling pathway either by changing intracellular calcium concentration ([Ca2+]i) via activation of its G-protein coupled membrane receptors, or through a direct interaction with CaM. In this study, although melatonin alone had no effect on basal [Ca2+]i in MCF-7 cells, it significantly enhanced the elevation of [Ca2+]i induction by extracellular adenosine triphosphate (ATP), which increases [Ca2+]i via the G protein-coupled P2y-purinoceptor and the phospholipase C (PLC) pathway. Pretreatment of MCF-7 cells with 10(-7) M melatonin increased the 10(-5) M ATP-induced [Ca2+]i peak change from 79.4 +/- 11.6 nM to 146.2 +/- 22.3 nM. Furthermore, without changing total cellular CaM levels, melatonin markedly increased the amount of membrane-bound CaM to 237 and 162% of control levels after I and 6 hr of treatment, respectively. Cytosolic CaM levels were also elevated to 172% of control after 6 hr of melatonin treatment. Correlative growth studies demonstrated that ATP (10(-5) M) can stimulate MCF-7 cell growth, that melatonin can suppress MCF-7 cell proliferation, but that pretreatment of MCF-7 cells with melatonin followed by ATP(10(-5) M), like 10(-4) M ATP can further suppress MCF-7 cell proliferation; this indicates that melatonin's potentiation of ATP induced [Ca2+]i may be above the threshold for cell growth. Given the important role of [Ca2+]i and CaM in tumor cell homeostasis and proliferation and melatonin's modulation of [Ca2+]i, melatonin's effects on the Ca2+/CaM signaling pathway may play an important role in mediating the growth-inhibitory effect of melatonin on MCF-7 human breast cancer cells.

Adenosine Triphosphate↗
PubMed2002

Adaptations of the renal microcirculation to hypertension.

Control of glomerular filtration involves sensitive regulation of glomerular filtration pressure over a widely varying range of systemic arterial pressures. This control is exerted through precise adjustments in preglomerular resistance involving numerous activation and feedback mechanisms. Under physiological conditions, these mechanisms succeed in maintaining renal blood flow and glomerular filtration rate in normal ranges and they provide protection of the glomerulus from elevated arterial pressure. However, under pathophysiological conditions, the accuracy of that regulation can be compromised. In hypertension, the efficiency with which preglomerular resistance is controlled is impaired. This can result in greater transmission of arterial pressure to glomerular capillaries, leading to inappropriately high glomerular filtration pressures and glomerular damage. Chronic exposure to hypertensive conditions can also lead to modification of the structure and/or function of the renal microvasculature as an adaptive response to the hypertension. Distinguishing adaptive, and thus protective, alterations in renal microvascular function from those that reflect deterioration of microvascular function is an important challenge. Inappropriate modifications in renal microvascular performance can lead to deterioration of glomerular function and can ultimately result in end-stage renal disease. This review will take a detailed look at the alterations in autoregulatory, vasoconstrictor, and vasodilatory responsiveness of the renal microcirculation during hypertension. It is anticipated that a more thorough understanding of the renal microcirculatory adaptations to hypertension will lead to better therapeutic approaches to managing hypertension while at the same time providing better protection to long term kidney function.

Adaptation, Physiological↗
PubMed2002

P2 receptor-mediated afferent arteriolar vasoconstriction during calcium blockade.

Experiments were performed to determine the role of L-type calcium channels on the afferent arteriolar vasoconstrictor response to ATP and UTP. With the use of the blood-perfused juxtamedullary nephron technique, kidneys were perfused at 110 mmHg and the responses of arterioles to alpha,beta-methylene ATP, ATP, and UTP were determined before and during calcium channel blockade with diltiazem. alpha,beta-Methylene ATP (1.0 microM) decreased arteriolar diameter by 8 +/- 1% under control conditions. This response was abolished during calcium channel blockade. In contrast, 10 microM UTP reduced afferent arteriolar diameter to a similar degree before (20 +/- 4%) and during (14 +/- 4%) diltiazem treatment. Additionally, diltiazem completely prevented the vasoconstriction normally observed with ATP concentrations below 10 microM and attenuated the response obtained with 10 microM ATP. These data demonstrate that L-type calcium channels play a significant role in the vasoconstrictor influences of alpha,beta-methylene ATP and ATP but not UTP. The data also suggest that other calcium influx pathways may participate in the vasoconstrictor response evoked by P2 receptor activation. These observations support previous findings that UTP-mediated elevation of intracellular calcium concentration in preglomerular vascular smooth muscle cells relies primarily on calcium release from intracellular pools, whereas ATP-mediated responses involve both voltage-dependent calcium influx, through L-type calcium channels, and the release of calcium from intracellular stores. These results support the argument that P2X and P2Y receptors influence the diameter of afferent arterioles through activation of disparate signal transduction mechanisms.

Adenosine Triphosphate↗