sq-23377 and Hypertension

Enhanced Na+/H+ exchange has been reported to be increased in patients with essential hypertension. However, early variations of intracellular pH, although influenced by the antiport, are only partially dependent on the exchange. In this study, we measured the initial platelet pH response to agonists in a group of untreated subjects with essential hypertension (EH, n = 24) and in a group of age- and sex-matched normotensive control subjects (CS, n = 24). Intracellular pH was measured with the specific fluorescence indicator 2'7'bis(carboxyethyl)-5,6-carboxyfluorescein. Measurements were performed on platelets in the presence or absence of extracellular calcium, in a carbonate-free medium. Intracellular calcium was measured by the Fura 2 method. Mean pH values were slightly higher in the platelets of EH (7.469 +/- 0.017 U) compared with CS (7.423 +/- 0.012 U, P < .05), although there was a substantial overlap. When stimulated with physiologic agonists ADP and thrombin and with the calcium ionophore ionomycin, a biphasic response consisting of early acidification followed by alkalinization was observed, the second phase not being detectable with ADP. The initial acidification was greater in EH, particularly with ADP (EH, -0.046 +/- 0.002 U; CS, -0.036 +/- 0.002 U, P < .001) and with ionomycin (EH, -0.074 +/- 0.007 U; CS, -0.051 +/- 0.005 U, P < .05). This acidification proved in some way calcium dependent, as it was reduced in the absence of extracellular calcium (EGTA) in both EH and CS. After incubation with amiloride a further decrease in intracellular pH, more marked in EH, was observed. Alkalinization induced by thrombin was increased in EH (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine Diphosphate; Adult; Blood Platelets; Calcium; Cytosol; Egtazic Acid; Female; Fluoresceins; Fluorescent Dyes; Humans; Hydrogen-Ion Concentration; Hypertension; Ionomycin; Male; Middle Aged; Platelet Activation; Thrombin

NADPH oxidases are the major sources of reactive oxygen species in cardiovascular, neural, and kidney cells. The NADPH oxidase 5 (NOX5) gene is present in humans but not rodents. Because Nox isoforms in renal proximal tubules (RPTs) are involved in the pathogenesis of hypertension, we tested the hypothesis that NOX5 is differentially expressed in RPT cells from normotensive (NT) and hypertensive subjects (HT). We found that NOX5 mRNA, total NOX5 protein, and apical membrane NOX5 protein were 4.2±0.7-fold, 5.2±0.7-fold, and 2.8±0.5-fold greater in HT than NT. Basal total NADPH oxidase activity was 4.5±0.2-fold and basal NOX5 activity in NOX5 immunoprecipitates was 6.2±0.2-fold greater in HT than NT (P=<0.001, n=6-14/group). Ionomycin increased total NOX and NOX5 activities in RPT cells from HT (P<0.01, n=4, ANOVA), effects that were abrogated by pre-treatment of the RPT cells with diphenylene-iodonium or superoxide dismutase. Silencing NOX5 using NOX5-siRNA decreased NADPH oxidase activity (-45.1±3.2% vs. mock-siRNA, n=6-8) in HT. D1-like receptor stimulation decreased NADPH oxidase activity to a greater extent in NT (-32.5±1.8%) than HT (-14.8±1.8). In contrast to the marked increase in expression and activity of NOX5 in HT, NOX1 mRNA and protein were minimally increased in HT, relative to NT; total NOX2 and NOX4 proteins were not different between HT and NT, while the increase in apical RPT cell membrane NOX1, NOX2, and NOX4 proteins in HT, relative to NT, was much less than those observed with NOX5. Thus, we demonstrate, for the first time, that NOX5 is expressed in human RPT cells and to greater extent than the other Nox isoforms in HT than NT. We suggest that the increased expression of NOX5, which may be responsible for the increased oxidative stress in RPT cells in human essential hypertension, is caused, in part, by a defective renal dopaminergic system.

Topics: Cells, Cultured; Gene Expression Regulation, Enzymologic; Humans; Hypertension; Ionomycin; Isoenzymes; Kidney Tubules, Proximal; Membrane Proteins; NADPH Oxidase 5; NADPH Oxidases; Onium Compounds; Oxidative Stress

Diabetic nephropathy is associated with progressive renal damage, leading to impaired function and end-stage renal failure. Secondary hypertension stems from a deranged ability of cells within the kidney to resolve and appropriately regulate sodium resorption in response to hyperglycaemia. However, the mechanisms by which glucose alters sodium re-uptake have not been fully characterised.. Here we present RT-PCR, western blot and immunocytochemistry data confirming mRNA and protein expression of the serum and glucocorticoid inducible kinase (SGK1) and the alpha conducting subunit of the epithelial sodium channel (ENaC) in a model in vitro system of the human cortical collecting duct (HCD). We examined changes in expression of these elements in response to glucose challenge, designed to mimic hyperglycaemia associated with type 2 diabetes mellitus. Changes in Na+ concentration were assessed using single-cell microfluorimetry.. Incubation with glucose, the Ca2+-ionophore ionomycin and the cytokine TGF-beta1 were all found to evoke significant and time-dependent increases in both SGK1 and alphaENaC protein expression. These molecular changes were correlated to an increase in Na+-uptake at the single-cell level.. Together these data offer a potential explanation for glucose-evoked Na+-resorption and a potential contributory role of SGK1 and ENaCs in development of secondary hypertension, commonly linked to diabetic nephropathy.

Topics: Blotting, Western; Cells, Cultured; Diabetes Mellitus; Epithelial Sodium Channels; Glucose; Humans; Hyperglycemia; Hypertension; Immediate-Early Proteins; Ionomycin; Kidney Tubules, Collecting; Protein Serine-Threonine Kinases; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sodium; Transforming Growth Factor beta1

Abnormal Ca2+ handling and enhanced aggregation response have been reported in platelets from spontaneously hypertensive rats (SHR) and patients with essential hypertension, and thought to be involved in the progression of target organ damage of hypertension. It is important to examine whether antihypertensive therapy can improve the abnormal platelet response in hypertension. We investigated the effect of antihypertensive treatment such as amlodipine and cilazapril on Ca2+ handling and aggregation response in SHR platelets. Four-week-old male SHR were divided into three groups. Each group was treated with amiodipine (A: 10 mg/kg/day), cilazapril (C: 10 mg/kg/day) or vehicle (V) for 8 weeks by gavage. At 12-week-old, platelet [Ca2+]i was measured with fura-2 in each group of SHR and age-matched Wistar-Kyoto rats (WKY) as normal control. Systolic blood pressure in amlodipine and cilazapril treated groups were similar with WKY and significantly lower than vehicle treated group (A: 124 +/- 9, C: 126 +/- 9, WKY: 122 +/- 10 and V: 180 +/- 9 mmHg, respectively). The basal [Ca2+]i in the three groups of SHR were similar and higher than WKY (A: 47 +/- 1.7, C: 47 +/- 1.2, V: 48 +/- 3.9 and WKY: 40 +/- 4.0 nmol/l, respectively). There were no significant differences in thrombin (0.1 U/ml)-stimulated [Ca2+]i rise in the presence or absence of extracellular Ca2+ among the three groups of SHR and these were higher than WKY. Intracellular Ca2+ discharge capacity, assessed by the ionomycinstimulation was similar in the all groups. Thrombin-induced maximum platelet aggregation responses in the three groups of SHR were similar and higher than WKY. The antihypertensive treatment of Ca2+ antagonist or ACE inhibitor gave no change in intraplatelet Ca2+ metabolism in SHR. These results support the hypothesis that an abnormal Ca2+ handling in SHR platelet is genetically determined and not improved by hypotensive therapy.

Topics: Amlodipine; Angiotensin-Converting Enzyme Inhibitors; Animals; Antihypertensive Agents; Blood Platelets; Blood Pressure; Body Weight; Calcium; Calcium Channel Blockers; Cilazapril; Cytosol; Heart Rate; Hypertension; Ionomycin; Male; Platelet Aggregation; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Thrombin

Mesangial cells (MC) are considered to play an important role in the development of hypertension. The purpose of this study was to characterize the effects of cytosolic Ca2+ on membrane voltage and conductance of MC using stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY). We applied the patch-clamp technique in the whole-cell configuration to measure membrane potential (Vm) and ion currents. There was no significant difference in resting Vm values between MC from WKY and SHRSP. The cytosolic Ca2+ increase induced membrane depolarization and the increase of Cl- currents in MC from WKY but not in MC from SHRSP. On the other hand, the Ca2+ increase induced membrane hyperpolarization and the increase of K+ currents in MC from SHRSP but not in MC from WKY. Such differences between MC from two rat strains may play an important role in the alterations in renal hemodynamics observed in hypertension.

Topics: Animals; Calcium; Cells, Cultured; Cerebrovascular Disorders; Chloride Channels; Disease Models, Animal; Electric Conductivity; Glomerular Mesangium; Hypertension; Ionomycin; Membrane Potentials; Patch-Clamp Techniques; Potassium Channels; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Time Factors

The main aims of this work were to examine in women: the relationship between the freely exchangeable Ca2+ (FECa2+) in the dense tubules and the activity of the sarco(endo)plasmic reticulum (SER) Ca2+-ATPase (SERCA) in platelets, and the relationship of these parameters with blood pressure and serum lipoproteins. Platelets from 14 white and 13 black women in good health were studied. The FECa2+ was measured as the ionomycin-evoked Ca2+ release (in the presence of thapsigargin) in Ca2+-free medium. SERCA activity was measured as the thapsigargin sensitive, Ca2+ dependent and ouabain resistant, ATP hydrolyses in platelet membranes. Relative expressions of SERCA 2 and 3 isoforms and Ras-related protein (Rap) 1 in platelet membranes were determined by Western immunoblots. Highly significant correlations were observed for FECa2+ in the dense tubules with: 1) the maximal reaction velocity (Vmax) of the SERCA (r = 0.592, P = .0014), and 2) Rapl (r = 0.551, P = .0035). In addition, negative correlations were observed between FECa2+ in the dense tubules and age. No correlations were observed for these variables with blood pressure or serum lipoproteins. We conclude the FECa2+ and the Vmax of the SERCA are reliable indicators of Ca2+ load in platelets from women. However, in women, unlike previous observations in men, these platelet parameters are not correlated with blood pressure and serum lipoproteins.

Topics: Adult; Black People; Blood Platelets; Blood Pressure; Blotting, Western; Calcium; Calcium-Transporting ATPases; Cell Membrane; Cytosol; Enzyme Inhibitors; Female; GTP-Binding Proteins; Humans; Hypertension; Ionomycin; Ionophores; Lipoproteins; rap GTP-Binding Proteins; Sarcoplasmic Reticulum; Transcription Factors; White People

Hypertension is characterized by a complex mode of inheritance, consisting of the accumulation and interaction of major and minor genes. The existence of a single major gene locus (ht) has been demonstrated in the backcross analysis of spontaneously hypertensive rats (SHR) and normotensive Donryu rats. Intracellular Ca2+ concentration ([Ca2+]i) determines the tonus of vascular smooth muscle. It has been hypothesized that abnormal Ca2+ transport is an inheritable trait with profound influence on the development of hypertension. Backcross analysis between SHR and Donryu rats was performed to demonstrate ht and to dissect polygenic hypertensive traits through ht and abnormal intracellular Ca2+ metabolism. Among the parental strains, systolic blood pressure and thrombin-stimulated [Ca2+]i in platelets were significantly greater in SHR than in Donryu and F1 rats. The backcrossed rats were distributed into two clusters on a scattergram of blood pressure versus [Ca2+]i, demonstrating the existence of ht. The blood pressure level was correlated with thrombin-stimulated [Ca2+]i in each cluster. Increased [Ca2+]i in platelets was not coinherited with ht and was considered to be a minor inheritable hypertensive trait discriminated from ht. Therefore, [Ca2+]i in platelets is an inadequate marker for searching ht.

Topics: Animals; Blood Platelets; Blood Pressure; Calcium; Calcium Channel Agonists; Crosses, Genetic; Fura-2; Genes; Hypertension; Ionomycin; Ionophores; Rats; Rats, Inbred SHR

We have reported that cytosolic Ca2+ concentration ([Ca2+]i) is increased in platelets from spontaneously hypertensive rats (SHR) in both basal and thrombin-stimulated conditions. To determine whether the correlation between blood pressure and cellular Ca2+ metabolism exists in stroke-prone SHR (SHRSP), we investigated Ca2+ handling using fura 2 and aggregation response in platelets of 12- to 13-week-old male SHRSP, SHR, and Wistar-Kyoto rats (WKY). Systolic pressure was highest in SHRSP and lowest in WKY (213 +/- 8, 172 +/- 7, and 135 +/- 5 mm Hg, respectively). Basal [Ca2+]i was significantly higher in SHR than WKY (45.9 +/- 4.5 versus 41.2 +/- 4.8 nmol/L, P<.05), and that in SHRSP (40.2 +/- 2.8 nmol/L) was similar to that in WKY. Thrombin (0.1 IU/mL)-stimulated [Ca2+]i rise was greater in SHR and smaller in SHRSP than in WKY in the presence of extracellular Ca2+ (530 +/- 50 and 408 +/- 52 versus 475 +/- 50 nmol/L, respectively; P<.05). The recovery rate from the peak [Ca2+]i response to thrombin was greatest in SHRSP and least in WKY. Ionomycin (5 micromol/L)-stimulated [Ca2+]i rise was similar in WKY, SHR, and SHRSP (731 +/- 97, 743 +/- 88, and 683 +/- 70 nmol/L, respectively). Thrombin-induced maximum platelet aggregation response was higher in SHR and lower in SHRSP than WKY (82 +/- 4 percent and 61 +/- 15 percent versus 73 +/- 6 percent, respectively; P<.05). In contrast to SHR, basal [Ca2+]i in SHRSP was similar to that in WKY, and thrombin-stimulated [Ca2+]i was attenuated. These result suggest that platelet Ca2+ handling differs between SHR substrains and that an increased [Ca2+]i is not obligatory in genetically hypertensive rats.

Topics: Animals; Blood Platelets; Blood Pressure; Calcium; Cerebrovascular Disorders; Cytosol; Fura-2; Hypertension; Ionomycin; Male; Platelet Aggregation; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Thrombin

The aim of the present work was to characterize angiotensin II (ANG II) receptors and their effect on intracellular free Ca2+ concentration ([Ca2+]i) in proliferating aortic smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Independently from the proliferating state of cultures, apparent affinities of ligands (ANG II > losartan > > CGP-42112A) were consistent with the presence of AT1 receptors in primary cells from SHR and WKY. In proliferating cultures, increases in [Ca2+]i elicited by ANG II (100 nM) were dramatically attenuated or abolished in VSMCs from both strains compared with confluent and postconfluent cultures. Ca2+ releases induced by ionomycin and by ANG II in the absence of extracellular Ca2+ were also impaired in proliferating cultures. In addition, no significant strain difference was found in proliferating cultures with respect to ANG II receptor density, basal [Ca2+]i, and ANG II-induced increases in [Ca2+]i. However, ANG II receptor density significantly increased in SHR, but not in WKY VSMCs at postconfluence. Furthermore, basal [Ca2+]i was elevated in confluent and postconfluent cultures from SHR but not WKY. In confluent cultures, ANG II- and ionomycin-induced Ca2+ releases were enhanced in SHR VSMCs compared with WKY VSMCs. These results show that ANG II-induced Ca2+ release and ionomycin-sensitive Ca2+ stores are enhanced in SHR VSMCs but dramatically decreased in proliferating VSMC cultures from both strains. Mechanisms underlying these alterations remain to be defined. However, the results suggest that alterations in ANG II AT1 receptor density and in intracellular Ca2+ handling in confluent and postconfluent cultures are not associated with the proliferative phenotype of SHR VSMCs. In addition, no evidence for any change in ANG II receptor subtype associated with proliferation of VSMCs was found in either strain.

Topics: Angiotensin II; Animals; Aorta; Calcium; Cell Division; Hypertension; Intracellular Membranes; Ionomycin; Male; Muscle, Smooth, Vascular; Osmolar Concentration; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Angiotensin; Reference Values

To examine further the potential role of intracellular cations in hypertension a nested case-control study was carried out in conjunction with a population-based survey. Based on a house-to-house sampling scheme, 43 hypertensive and 56 normotensive black residents of Maywood, IL, were recruited. Free cytosolic calcium (Cai) and intracellular stores of calcium after stimulation with ionomycin were determined in platelets with the fluoroprobe Indo-I; intracellular sodium (Nai) measured at rest and after incubation with ouabain was estimated with SBFI. Cell sodium content was also assayed in erythrocytes. Resting Cai and Nai were not different in hypertensives compared with normotensives, although ionomycin-stimulated levels of Cai were correlated with systolic blood pressure (r = 0.3; P = 0.04). A consistent set of inter-relations among the various cation parameters was observed, lending support to the hypothesis that the cellular metabolism of sodium and calcium may be linked in the pathophysiological pathway to hypertension.

Topics: Adult; Aged; Black People; Calcium; Case-Control Studies; Cytosol; Female; Humans; Hypertension; Ionomycin; Ionophores; Male; Middle Aged; Reference Values; Sodium

In this study we have compared Ca2+ efflux in cultured aortic smooth muscle cells derived from male, 10-week-old spontaneously hypertensive and Wistar-Kyoto rats. The role of Ca(2+)-dependent protein kinase C and Ca2+ uptake in the regulation of the Ca2+ pump and Na(+)-Ca2+ exchange mediated Ca2+ efflux were investigated. Basal, angiotensin II, and ionomycin-stimulated Ca2+ effluxes were significantly higher in spontaneously hypertensive rats. Brief (5 min) or prolonged (3 h) incubation of the cells with 100 nmol/L 12-O-tetradecanoylphorbol-13-O-acetate (TPA), a protein kinase C stimulator, did not significantly affect the maximum Ca2+ efflux rate in either strain. However, the Ca2+ efflux rates at early timepoints in Wistar-Kyoto rats were increased by TPA, but not in spontaneously hypertensive rats. Incubation of cells with [45Ca]-labeled CaCl2 in balanced salt solution for 4 h led to greater Ca uptake in spontaneously hypertensive rats compared to Wistar-Kyoto controls. Verapamil (1 mumol/L) for 4 h reduced the cellular Ca content of spontaneously hypertensive rats by 30% to the level of Wistar-Kyoto rats; it also reduced the Ca content in Wistar-Kyoto rats, but to a lesser extent (18%). In parallel, Ca2+ efflux was also reduced by verapamil to a greater extent in spontaneously hypertensive rats than in Wistar-Kyoto rats. We conclude that Ca2+ efflux was enhanced in spontaneously hypertensive rats by a mechanism partly associated with greater Ca2+ uptake by a verapamil-sensitive pathway and possibly an alteration of protein kinase C regulation. However, an up-regulation of the number or efficiency of Ca2+ efflux sites may also significantly contribute as an adaptive response to enhanced Ca2+ influx.

Topics: Animals; Calcium; Calcium Channel Blockers; Calcium Radioisotopes; Cells, Cultured; Hypertension; Ionomycin; Male; Muscle, Smooth, Vascular; Rats; Rats, Inbred SHR; Tetradecanoylphorbol Acetate; Verapamil

1. Cytosolic free sodium concentration and sodium transport systems were measured in intact cultured vascular smooth muscle cells from spontaneously hypertensive rats of the Münster strain and from normotensive Wistar-Kyoto rats using the sodium-sensitive fluorescent dye sodium-binding benzofuran isophthalate. 2. Resting cytosolic free sodium concentration was significantly lower in vascular smooth muscle cells from spontaneously hypertensive rats than from Wistar-Kyoto rats (10.2 +/- 1.5 mmol/l, n = 26, versus 19.4 +/- 2.5 mmol/l, n = 20, P < 0.01). 3. Inhibition of Na+, K(+)-ATPase by ouabain caused a dose-dependent increase in cytosolic free sodium concentration in spontaneously hypertensive rats and Wistar-Kyoto rats. 4. Activation of Na(+)-Ca2+ exchange by ionomycin increased cytosolic free sodium concentration in both strains. However, the ionomycin-induced increase in cytosolic free sodium concentrations was significantly higher in vascular smooth muscle cells from spontaneously hypertensive rats than from Wistar-Kyoto rats (220 +/- 35% of the resting cytosolic free sodium concentration versus 148 +/- 27%; P < 0.05). The ionomycin-induced increase in cytosolic free sodium concentration was prevented in the absence of external sodium or by inhibition of Na(+)-Ca2+ exchange by NiCl2. 5. Activation of Na(+)-H+ exchange by intracellular acidification of vascular smooth muscle cells with propionic acid increased cytosolic free sodium concentration in each strain (19.6 +/- 5.7 versus 16.3 +/- 3.2 mmol/l). 6. It is concluded that concepts concerning the role of cytosolic free sodium concentration in the pathogenesis of primary hypertension need to be reinvestigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Cells, Cultured; Cytosol; Dose-Response Relationship, Drug; Hypertension; Ionomycin; Male; Muscle, Smooth, Vascular; Ouabain; Propionates; Rats; Rats, Inbred SHR; Rats, Wistar; Sodium

The aim of this study was to clarify the further details of calcium handling in hypertension.. By preserving the physiological environment of cell membrane, whole hearts were used for comparison of calcium flux between spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats.. Hearts from SHR and WKY rats were perfused with Krebs-Henseleit solution under constant flow and the effluent collected.. After labelling of the heart with 45Ca2+ (100 mumol/l), 45Ca2+ binding was found to be saturated, and washing with calcium-free perfusion solution showed two exponential curves for calcium dissociation, indicating a fast (alpha-) and slow (beta-) phase. The half-lives of the beta-phase for both 4- and 8-week-old SHR were significantly shorter than those for age-matched WKY. Also in this phase, infusion of non-radioactive Ca2+ caused a transient dose-dependent release of 45Ca2+. A significant reduction in the amount of 45Ca2+ release induced by 2 mmol/l Ca2+ was observed in both 4- and 8-week-old SHR compared with age-matched WKY rats. Infusion of lanthanum, caffeine, ionomycin (calcium ionophore) and treatment of the hearts with ethyleneglycol-bis-(beta-aminoethylether)-N,N,N,',N'-tetraac etic acid did not alter 45Ca2+ release by non-radioactive Ca2+. From these observations, 45Ca2+ is presumably released from the intracellular calcium pool, and not from extracellular binding sites or sarcoplasmic reticulum.. These findings suggest that an abnormal calcium-handling defect (enhanced calcium efflux and reduction of membrane-bound Ca2+) exists under physiological conditions before and after the onset of hypertension, and that this may be a primary characteristic of SHR.

Topics: Aging; Animals; Caffeine; Calcium; Calcium Radioisotopes; Egtazic Acid; Half-Life; Heart; Hypertension; In Vitro Techniques; Ionomycin; Lanthanum; Male; Myocardium; Rats; Rats, Inbred SHR; Rats, Inbred WKY

We previously reported an enhanced peak response of intracellular free Ca2+ to thrombin in platelets of spontaneously hypertensive rats in comparison with normotensive Wistar-Kyoto rats. In the present study, we compared the platelet intracellular Ca2+ response to the receptor-linked agonist thrombin with the response to the Ca2+ ionophore ionomycin. Basal intracellular Ca2+ was higher in hypertensive platelets as was leakage of fura-2. We confirmed the previous finding that the thrombin-induced intracellular Ca2+ peak is greater in platelets of hypertensive rats and noted that the rate of recovery from peak intracellular Ca2+ is significantly greater in this model. In contrast, the peak platelet intracellular Ca2+ response to ionomycin (50 nM and 5 microM) was not different between the two strains, and the rate of recovery from the peak response was only slightly depressed in hypertensive rats after the low dose of ionomycin. Internal Ca2+ discharge capacity, assessed by the intracellular Ca2+ response to a maximal dose of ionomycin in Ca(2+)-free medium, was not different between platelets of the two strains. Thus, activated platelet intracellular Ca2+ is not altered in the hypertensive rat when the nonphysiological ionophore ionomycin is used as agonist. However, a heightened intracellular Ca2+ response is observed when the receptor-mediated agonist thrombin is used. These results are consistent with the hypothesis that differences in receptor-linked second messenger pathways underlie the altered intracellular Ca2+ response in platelets of genetically hypertensive rats and may contribute to differences both in the mobilization of Ca2+ and in its fall.

Topics: Animals; Blood Platelets; Calcium; Dose-Response Relationship, Drug; Hypertension; Ionomycin; Male; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Signal Transduction; Thrombin

Using a Coulter-based cell sizing method, we have previously demonstrated that, in response to cytoplasmic acidification by 140 mmol/l sodium propionate, both the mean initial rate of amiloride-sensitive platelet volume swelling and the net volume change achieved at steady-state are greater in essential hypertensives than in normotensives. In the present study, we extend this observation by showing that, in response to graded propionate exposure (56-140 mmol/l), steady-state amiloride-sensitive volume responsiveness (as percentage increase over baseline) increases linearly, and the mean slope of the line relating amiloride-sensitive volume change and propionate concentration is increased in hypertensives (0.40 +/- 0.02 versus 0.32 +/- 0.02% per mmol/l propionate, P less than 0.003). In 56 mmol/l propionate, average amiloride-sensitive platelet swelling is significantly less in hypertensives than in normotensives (7.6 +/- 0.8 versus 11.1 +/- 0.9%, P less than 0.05), but in 140 mmol/l propionate, swelling is significantly increased in hypertensives (40.8 +/- 1.7 versus 36.2 +/- 1.5%, P less than 0.05). Since platelet intracellular calcium concentration is elevated in some hypertensives and Ca2+ is known to stimulate Na(+)-H+ antiport, the transport system that is the primary determinant of amiloride-sensitive cell swelling during propionate incubation, we studied the effects of the Ca2+ ionophore, ionomycin, on volume regulation. In both normotensives and hypertensives, ionomycin (2 x 10(-10 to 2 x 10(-7) mol/l) causes dose-related increases in amiloride-sensitive platelet swelling during graded propionate exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Amiloride; Blood Platelets; Calcium; Carrier Proteins; Female; Humans; Hydrogen-Ion Concentration; Hypertension; Ionomycin; Male; Propionates; Sodium-Hydrogen Exchangers

To test the hypothesis that an abnormality of the intracellular concentration of ionized calcium, [Ca2+]i, is associated with high blood pressure, we measured [Ca2+]i in the platelets of spontaneously hypertensive (SHR) and Wistar-Kyoto control (WKY) rats using the Quin 2 technique after separation of the platelets in calcium-free medium, during calcium repletion, and upon exposure to agonists which increase platelet [Ca2+]i (thrombin, adenosine diphosphate, serotonin and ionomycin). Despite clear-cut changes in [Ca2+]i during these manipulations, there were no differences between the SHR and WKY rats in baseline levels of [Ca2+]i or in the kinetics of changes in [Ca2+]i. These results do not support the hypothesis that high levels of [Ca2+]i at rest or abnormal kinetics of changes in [Ca2+]i play a pathophysiological role in the hypertension of SHR.

Topics: Adenosine Diphosphate; Animals; Blood Platelets; Blood Pressure; Calcium; Cytosol; Ethers; Hypertension; Ionomycin; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Serotonin; Thrombin