Intracellular calcium and sodium in hypertensive patients

Plasma Na-K Atpase Inhibitor Activity and Intracellular Ions during Hemodialysis

We have investigated the relationship between plasma Na-K ATPase inhibitor activity (EDLS) and intracellular ions in 37 uremic hemodialysed hypertensive patients, and in 20 normotensive non uremic controls (NC). As compared with the NC population, significantly enhanced values for erythrocyte (RBC) Na, Ca, platelet cytosolic Ca and EDLS were observed in all the uremic patients tested just before a dialysis session, as well as a decrease in RBC Ca ATPase and in the platelet pH. In uremia, significant correlations have been noted between RBC Na and platelet Ca (r = 0.6) or systolic BP (r = 0.45); between platelet Ca and systolic blood pressure (r = 0.8) or diastolic BP (r = 0.5) and between EDLS and RBC Na, Ca or platelet Ca (r = 0.5). Anti-hypertensive treatment has no influence on these parameters. During dialysis, a significant decrease has been noted in RBC Na, Ca, platelet Ca, SBP (only in untreated patients) and EDLS and an increase in RBC Ca ATPase and platelet pH. These modifications are significantly correlated with the weight change.

Glycine reduces platelet aggregation

It has been demonstrated that a wide variety of white blood cells and macrophages (i.e. Kupffer cells, alveolar and peritoneal macrophages and neutrophils) contain glycine-gated chloride channels. Binding of glycine on the receptor stimulates Cl(-) influx causing membrane hyperpolarization that prevents agonist-induced influx of calcium. Since platelet-aggregation is calcium-dependent, this study was designed to test the hypothesis that glycine would inhibit platelet aggregation. Rats were fed diets rich of glycine for 5 days, while controls received isonitrogenous valine. The bleeding time and ADP- and collagen-induced platelet aggregation were measured. Dietary glycine significantly increased bleeding time about twofold compared to valine-treated controls. Furthermore, the amplitude of platelet aggregation stimulated with ADP or collagen was significantly decreased in whole blood drawn from rats fed 2.5 or 5 % dietary glycine by over 50 %. Addition of glycine in vitro (1-10 mM) also blunted rat platelet aggregation in a dose-dependent manner. Strychnine, a glycine receptor antagonist, abrogated the inhibitory effect of glycine on platelet-aggregation in vitro suggesting the glycine works via a glycine receptor. Glycine also blunted aggregation of human platelets. Further, the glycine receptor was detected in both rat and human platelets by western blotting. Based on these data, it is concluded that glycine prevents aggregation of platelets in a dose-dependent manner via mechanisms involving a glycine receptor.

Chagas disease as a mechanistic model for testing a novel hypothesis

The association between depression and cardiovascular disease is well documented. Nevertheless, the process through which they are linked remains unknown, as does the direction of this relationship. Studies have suggested both that depression is a risk factor for heart disease and that heart disease is a risk factor for depression. A number of studies have established that a relationship exists between depression and inflammation, with alterations in the levels of inflammatory markers (IL-1, IL-6, TNF-alpha and others). Depressive symptoms have also been identified in many diseases characterized by inflammatory processes e.g. rheumatoid arthritis, bronchial asthma, diabetes, tuberculosis and cardiovascular diseases. In this brief viewpoint, we explain and propose how to use Chagas disease, a disorder characterized by inflammatory processes and leading to cardiovascular and autonomic problems, as a model for studying the directionality of the relationship between heart disease and depression.

New insights into the link between cardiovascular disease and depression

INTRODUCTION

Although the association between depression and cardiovascular disease (CVD) is well documented, the underlying mechanisms for this relationship remain unclear. In this paper, we present three possible models which account for the comorbidity between depression and cardiovascular disease.

MODELS

The first model outlines depression as a risk factor for CVD and the second model presents CVD as a risk factor for depression. The third model proposes a common underlying pathway related to the effects of chronic stress on the body in manifesting as depression or cardiovascular disease.

CONCLUSIONS

If the proposed model holds true, it may be possible that an intervention initiated before overt manifestations of CVD or depression become apparent, may delay or prevent the onset of these serious clinical entities.

Neuronal populations of rat cerebral cortex and hippocampus expressed a higher density of L-type Ca 2+ channel than corresponding cerebral vessels

Dihydropyridine (DHP)-type Ca2+ antagonists block primarily L-type Ca2+ channels and are used in the therapy of hypertension. They were also proposed for the treatment of several central nervous system disorders. In brain, these compounds bind both neuronal and vascular Ca2+ channels, but no studies have evaluated comparatively their density at neuronal and vascular level. This study has analyzed the pharmacological profile and the anatomical localization of L-type Ca2+ channels in rat frontal cortex, hippocampus and in forebrain pial and intracerebral arteries by radioligand binding assay and high resolution light microscope autoradiography. The DHP derivative [3H]nicardipine was used as a radioligand. Binding of [3H]nicardipine was consistent with the labeling of L-type Ca2+ channels. In frontal cortex, the highest density of binding sites was found in nerve cell body region, followed by the neuropil and the wall of intracerebral arteries. In hippocampus, the density of binding sites was higher in the nerve cell body region than in the neuropil of CA1, CA3, and CA4 subfields. In the dentate gyrus, a higher density of silver grains was developed in neuropil than in nerve cell body of granule neurons. With the exception of dentate gyrus, neuronal binding sites were more expressed than vascular binding sites in the hippocampus. In pial arteries [3H]nicardipine binding density decreased concomitant with the reduction of vessel diameter, whereas in intracerebral arteries [3H]nicardipine binding density displayed an opposite pattern. The above findings indicate that in brain the density of neuronal L-type Ca2+ channels was significantly higher than that of vascular ones. This may account for more pronounced neuronal than vascular effects after pharmacological manipulation of cerebral Ca2+ channels.

Dietary (n-3) polyunsaturated fatty acids exert antihypertensive effects by modulating calcium signaling in T cells of rats

After 10 wk of feeding an experimental diet enriched with (n-3) polyunsaturated fatty acids (PUFA), i.e., eicosapentaenoic acid [EPA, 20:5(n-3)] and [DHA, 22:6(n-3)] (EPAX), blood pressure in spontaneously hypertensive rats (SHR), but not in normotensive Wistar-Kyoto (WKY) rats was reduced relative to rats fed an unsupplemented control diet. Concanavalin A-stimulated T-cell proliferation was diminished in both strains of rats fed the PUFA/EPAX diet. The experimental diet lowered secretion of interleukin-2 in SHR, but not in WKY rats compared with rats fed the control diet. To determine whether there was a defect in calcium homeostasis in T cells during hypertension, we employed the following agents: caffeine, which recruits calcium from the cytosolic Ca(2+)-induced Ca(2+)-release pool; ionomycin, which at low concentrations opens calcium channels; and thapsigargin (TG), which mobilizes [Ca(2+)]i from the endoplasmic reticulum (ER) pool. Caffeine-induced increases in [Ca(2+)]i were not modified by the PUFA/EPAX diet. The ionomycin-induced increases in [Ca(2+)]i in T cells from SHR were greater than in those from WKY rats; consumption of the PUFA/EPAX diet did not modify Ca(2+) influx in cells of either strain. The TG-induced increases in [Ca(2+)]i in T cells from SHR were greater than those in cells from WKY rats. Interestingly, consumption of the experimental diet reduced TG-evoked increases in [Ca(2+)]i in T cells from SHR and increased those in T cells from WKY rats, indicating that the PUFA/EPAX diet could reverse the calcium mobilization from the ER pool in T cells. These results suggest that (n-3) PUFA exert antihypertensive effects and modulate T-cell calcium signaling during hypertension in rats.

Influence of age on L-type Ca2+ channels in the pulmonary artery and vein of spontaneously hypertensive rats

The influence of age on the density and localization of L-type Ca2+ channels was studied during development of hypertension in the pulmonary artery and vein of spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats by radioligand binding assay and light microscope autoradiography. SHR were examined at 6 weeks (juvenile, pre-hypertensive stage), 12 weeks (young, developing hypertension) and 24 weeks (mature, established hypertension). The dihydropyridine-type Ca2+ antagonist [3H]nicardipine was used as a radioligand. It was bound specifically to sections of rat pulmonary artery and vein. Dissociation constant (Kd) values were similar in WKY rats and SHR, whereas maximum density of binding sites (Bmax) values increased in SHR in comparison with WKY rats. This increase was noticeable from the pre-hypertensive phase. The pharmacological profile of [3H]nicardipine binding was similar in different age groups of either normotensive and hypertensive rats. Quantitative analysis of autoradiographs from SHR revealed a progressive increase of silver grains in smooth muscle of tunica media and to a lesser extent in the adventitia of pulmonary artery but not of pulmonary vein from pre-hypertensive stage to developing hypertension. No further changes were observed in established hypertension. The above data indicate that the density of L-type Ca2+ channels of pulmonary arteries is increased in SHR. This augmentation after the pre-hypertensive phase suggests the occurrence of dysregulation of Ca2+ handling in the pulmonary vasculature of developing SHR.

Calcium metabolism in pre-eclampsia

OBJECTIVES

To study calcium metabolism in pre-eclampsia and normotensive gravid women.

METHOD

Ten milliliters of heparinized blood samples and 24-h urine samples were collected from 50 pre-eclamptic and 50 normotensive primigravidae. Blood samples were studied for calcium uptake, intracellular calcium level and calcium-dependent adenosine triphosphatase activity of red blood cell ghost. Urinary calcium excretion was estimated from the 24-h urine samples. These values were compared in the two groups.

RESULTS

The mean gestational age at recruitment was similar in both the groups. The mean maternal age was 24.28 +/- 2.41 years in pre-eclamptic and 23.48 +/- 4.16 years in normotensive women. In pre-eclampsia 24-h urinary calcium excretion (71.20 +/- 22.95 mg/day) and calcium-dependent ATPase activity (10.78 +/- 2.40 nmol/Pi/mg protein/min) was significantly lower compared to normotensive primigravidae (calcium excretion = 189.24 +/- 57.06 mg/day; Ca2+-dependent ATPase = 12.64 +/- 2.42 nmolPi/mg /protein per min; P < 0.001). Intracellular calcium levels and calcium uptake at 10 min by red blood cells were significantly higher in pre-eclampsia (P < 0.05). Calcium uptake by red blood cells at 20 and 30 min was similar in both groups.

CONCLUSION

Pre-eclampsia is associated with increased levels of intracellular calcium, decreased calcium-dependent ATPase activity of erythrocytes and hypocalciuria.

Parameters of lymphocyte Na+-Ca2+ regulation and blood pressure: the gender effect

Alterations in cellular Ca2+ and Na+ regulation play a role in the pathogenesis of essential hypertension. Using peripheral lymphocytes from 68 normal persons, we observed the following relationships for major cellular Ca2+ regulatory parameters. Among men and women, Na+-Ca2+ exchanger activity was positively correlated with the resting cytosolic free Ca2+ ([Ca2+]c) (r=0.43, P=0.0003), and the resting [Ca2+]c was positively correlated with cytosolic Na+ ([Na+]c) (r=0.50, P=0.0001). For men only, store-operated Ca2+ entry was positively correlated with Na+-Ca2+ exchanger activity (r=0.63, P=0.0001). In addition, systolic and diastolic blood pressures were positively correlated with [Na+]c in men (r=0.53, P=0.001, and r=0. 41, P=0.017, respectively) but not in women (r=0.30, P=0.088, and r=0.24, P=0.17, respectively). Some of the relationships between cellular and blood pressure parameters were confounded by serum triglycerides. These observations indicate a gender effect on cellular Ca2+-Na+ regulation and its relationship with blood pressure.

Erythrocytic protein kinase C activity in primary hypertension

OBJECTIVES

Increased protein kinase C activity has been reported in erythrocytes from patients with primary hypertension and also from hypertensive rats. In this phenomenological study, we investigated whether a possible increased activity was the result of an augmented amount of enzyme molecules or a more active enzyme.

DESIGN

Collect blood samples, separate erythrocytes from other blood cells. After partial purification of protein kinase C in the erythrocyte lysate, assay the enzyme activity under optimal conditions using a specific peptide substrate.

SETTING

Central Hospital in Eskilstuna and University Hospital in Uppsala, Sweden.

SUBJECTS

Healthy individuals: 47 persons (20 women and 27 men). Ten patients with untreated primary hypertension.

MAIN OUTCOME MEASURES

Erythrocytes were separated from leucocytes and platelets by passing through a cellulose column followed by repeated washings. Some proteins in the erythrocyte lysate interfering with protein kinase C assay were removed by chromatography on DEAE-cellulose.

RESULTS

The mean protein kinase C activity in erythrocytes from healthy individuals was 0.18 +/- 0.02 pmol [32P]phosphate min(-1) x 10(6) cells, regardless of sex and age. The corresponding value for patients with primary hypertension was 0.16 +/- 0.04 pmol [32P]phosphate min(-1) x 10(6) cells.

CONCLUSIONS

The amount of protein kinase C, measured as the activity at optimal assay conditions, in erythrocytes from patients with primary hypertension is not critical for the development of moderate hypertension.

Ca2+ in the dense tubules: a model of platelet Ca2+ load

In this work, we explored the relationship between the freely exchangeable Ca2+ (FECa2+) in the dense tubules (DT) and the sarco(endo)plasmic reticulum (SER) Ca2+-ATPase (SERCA) in circulating human platelets and examined the relationship between blood pressure (BP) and these platelet parameters. Studying platelets from 32 healthy men, we showed that the maximal reaction velocity (Vmax) of the SERCA significantly correlated with FECa2+ in the DT and with the protein expressions of SERCA 2 and 3. BP positively correlated with both the Vmax of the SERCA (r=.462, P=.010) and the FECa2+ sequestered in the DT (r=.492, P=.005). The relationships between these platelet Ca2+ parameters and BP were in part confounded by increased levels of serum triglycerides and diminished HDL cholesterol with a higher BP. No correlation was observed between the resting cytosolic Ca2+ and BP. Collectively, these findings indicate that (1) an increase in the cellular Ca2+ load in platelets is expressed by a higher activity of the SERCA and an increase in the expressions of SERCA 2 and 3 proteins, coupled with an increase in the FECa2+ in the DT, and (2) a higher BP is associated with an increase in platelet Ca2+ load in human beings, expressed by a rise in the FECa2+ in the DT and the upregulation of SERCA activity.

Platelet cytosolic calcium concentration in patients with liver cirrhosis. Relationship with hepatic and systemic hemodynamics

BACKGROUND/AIMS

Due to structural and functional similarities between platelets and vascular smooth muscle cells, platelet cytosolic calcium concentration ([Ca2+]i) has been suggested to be a useful tool to study regulatory mechanisms of peripheral vascular tone. The aim of the present study was to investigate platelet [Ca2+]i in patients with cirrhosis and whether this parameter is related with the systemic and splanchnic vasodilatation found in these patients.

METHODS

Seventeen patients with cirrhosis and eight age- and sex-matched controls were studied. Mean arterial pressure, cardiac output, femoral blood flow and basal and thrombin-stimulated platelet [Ca2+]i were measured. Cardiac output (thermal dilution), azygos blood flow, hepatic venous pressure gradient and hepatic blood flow were also measured in patients with cirrhosis.

RESULTS

Patients with cirrhosis had severe portal hypertension and a significantly higher cardiac output and femoral blood flow and a significantly lower systemic and femoral vascular resistance than controls. Patients with cirrhosis had a lower basal platelet [Ca2+]i than normal subjects. However, there was no relationship between platelet [Ca2+]i and any of the hemodynamic parameters that evaluate systemic or splanchnic vasodilatation.

CONCLUSIONS

This study shows that cirrhotic patients with portal hypertension have a significant reduction in platelet basal [Ca2+]i. The lack of correlation between platelet [Ca2+]i and hepatic and systemic hemodynamics does not support the use of platelet [Ca2+]i as a model to study mechanisms involved in the pathophysiology of the hyperdynamic circulation associated to portal hypertension.

Effects of nisoldipine on cytosolic calcium, platelet aggregation, and coagulation/fibrinolysis in patients with coronary artery disease

The effect of nisoldipine, a dihydropyridine Ca2+ antagonist, on the platelet cytosolic Ca2+ concentration ([Ca2+]i), platelet aggregation, and various coagulation and fibrinolysis parameters was assessed in normotensive patients with coronary artery disease (CAD). Eleven patients with angiographically confirmed CAD (4 men, 7 women aged 67.3 +/- 5.4 years) were administered nisoldipine at 10 mg/day for two weeks. The [Ca2+]i was determined by use of fura2-loaded platelets, platelet aggregation was measured with an aggregometer, and coagulation/fibrinolysis parameters were measured by standard methods. Nisoldipine did not significantly affect blood pressure or heart rate. However, the [Ca2+]i decreased significantly (P<0.05) and platelet aggregation was also significantly inhibited. Plasma D-dimer levels decreased significantly (P<0.01). Thus, nisoldipine not only suppressed platelet activation but also affected the coagulation system, suggesting that it is not only a vasodilator and platelet inhibitor but also an antithrombotic agent.

Intracellular free calcium abnormalities in fibroblasts from non-insulin-dependent diabetic patients with and without arterial hypertension

As arterial hypertension is frequently associated with diabetes, it is possible that altered intracellular free calcium ([Ca2+]i) handling, as reported in non-insulin-dependent diabetic patients, is accounted for by abnormalities caused by hypertension rather than diabetes. Our aim was to investigate [Ca2+]i transients triggered by two extracellular agonists, bradykinin and angiotensin II, with or without chronic insulin exposure, in cultured skin fibroblasts from 10 normotensive and 10 hypertensive non-insulin-dependent patients, matched for age, body mass index, and metabolic control, with fibroblasts from 10 healthy control subjects. Long-term cultured fibroblasts were loaded with fura 2-AM for measurement of [Ca2+]i. Resting [Ca2+]i levels were similar in the three groups of subjects. [Ca2+]i spikes stimulated by angiotensin II (0.1 mumol/L) and bradykinin (1 mumol/L) were significantly greater in hypertensive non-insulin-dependent diabetic patients (216 +/- 43 and 374 +/- 39 nmol/L, respectively) than in normotensive patients (174 +/- 16 and 267 +/- 55 nmol/L) and control subjects (188 +/- 29 and 320 +/- 78 nmol/L). Also, ionomycin evoked a greater [Ca2+]i response in hypertensive than normotensive non-insulin-dependent diabetic patients and in control subjects. Chronic insulin exposure increased by 70% to 90% the [Ca2+]i response to both angiotensin II and bradykinin in control subjects and normotensive non-insulin-dependent diabetic patients but not in hypertensive patients. The presence of abnormalities in [Ca2+]i transients in fibroblasts from only hypertensive non-insulin-dependent diabetic patients supports the possibility that these defects are a feature of concomitant arterial hypertension rather than of diabetes or its disturbed metabolic milieu.

Secondary hypertension: evaluation and treatment

Most patients with hypertension in the United States have essential (primary) hypertension (95%), the cause of which is unknown. The remaining 5% of adults with hypertension have the secondary form of hypertension, the cause and pathophysiologic process of which are known. Internists and other primary care physicians refer to this as treatable or curable hypertension, because the hypertension can be managed or even controlled with medications. Similarly, the condition is called surgical hypertension by surgeons in the belief that once the cause is determined and identified, surgical intervention will result in cure of hypertension. Secondary causes of hypertension include renal parenchymal disease, renovascular diseases, coarctation of the aorta, Cushing's syndrome, primary hyperaldosteronism, pheochromocytoma, hyperthyroidism, and hyperparathyroidism. Occasionally included in this category are alcohol- and oral contraceptive-induced hypertension and hypothyroidism, but these conditions are not discussed herein. The evaluation of secondary hypertension is of interest and can bring together different facets of anatomy, physiology, pharmacology, and radiology in the medical and surgical treatment of these disorders. Despite enthusiasm that can be generated in the evaluation of these conditions, evaluation can be expensive and should not be conducted for all patients with hypertension. Features that aid in the diagnosis of secondary hypertension include the following: 1. Onset of hypertension before the age of 20 or after the age of 50 years. The presence of hypertension at a young age may suggest coarctation of the aorta, fibromuscular dysplasia, or an endocrine disorder. Hypertension found for the first time after the age of 50 years may suggest the presence of renovascular hypertension caused by atherosclerosis. 2. Markedly elevated blood pressure or hypertension with severe end-organ damage, as in grade III or IV retinopathy. These findings suggest the presence of renovascular hypertension or pheochromocytoma. 3. Specific body habitus and ancillary physical findings. For example, truncal obesity and purple striae occur with hypercortisolism, and exophthalmos is associated with hyperthyroidism. 4. Resistant or refractory hypertension (poor response to medical therapy usually necessitating use of more than three antihypertensive medications from three different classes). 5. Specific biochemical test that suggest the existence of certain disorders, such as hypercalcemia in hyperparathyroidism, hyperglycemia in Cushing's syndrome and pheochromocytoma, and unprovoked hypokalemia with renin-producing tumors, primary hyperaldosteronism, or renin-mediated renovascular hypertension. 6. Other characteristics that may suggest secondary hypertension such as abdominal diastolic bruits (renovascular hypertension), decreased femoral pulses (coarctation of the aorta), or bitemporal hemianopias (Cushing's disease). A combination of a good history and physical examination, astute observation, and accurate interpretation of available data usually are helpful in the diagnosis of a specific causation.

Intracellular cations and hypertension in blacks

Considerable attention has been focused in recent years on the role of intracellular ions in the pathophysiology of hypertension in African Americans. Following the identification of marked differences in red cell sodium content and sodium-lithium counter-transport between blacks and whites, the hypothesis emerged that cation metabolism at the cellular level might account for part of the ethnic difference in susceptibility to hypertension. Unfortunately, findings in the red cell have not significantly increased our understanding of the physiologic pathways and may prove to be anomalous. Interest has recently shifted to calcium metabolism, because of its greater physiologic relevance, and a new series of questions are being defined. With the development of fluoroprobes to measure sodium and calcium simultaneously, wider application of pharmacologic agonists and the use of single cell techniques have provided a new direction for this field. Whether the ethnic contrasts observed for sodium in the red cell can be reproduced in platelets remains to be seen. It may be that the earlier red cell differences were epiphenomena, unrelated to the control of blood pressure, and that the more closely one approaches basic physiologic mechanisms, the greater the cross-ethnic group similarity. Rather than drawing attention to unusual phenotypic characteristics, the study of hypertension in blacks may be more instructive for the insight it provides into the basic physiology of this disorder, common to all ethnic groups.

Hereditary intermediate phenotypes in African American hypertension

OBJECTIVE

Essential hypertension is a heterogeneous and multifactorial disorder and is at least twice as frequent among African Americans as in the general population. Inheritance of high blood pressure is complex, with the gene(s) responsible for hypertension still remaining elusive. A useful strategy for investigating the heritability of hypertension is to evaluate 'intermediate phenotypes'--simple Mendelian or monogenic traits that are associated with hypertension. These intermediate steps may identify potential pathophysiological factors that antedate the development of high blood pressure and suggest candidate genes. We are attempting to identify and characterize several such intermediate phenotypes, in particular as these might apply to hypertension in African Americans.

METHODS

We studied several physiological and biochemical candidate intermediate phenotypes in untreated black and white patients with essential hypertension and in their normotensive counterparts stratified by genetic risk of hypertension.

RESULTS AND CONCLUSIONS

Promising intermediate phenotypes, which may be useful for studies in African American families, include baroreceptor sensitivity to low and high pressure stimuli, cold pressor test responses, and biochemical markers such as plasma chromogranin A, dopamine-beta-hydroxylase and urinary kallikrein excretion. Identification of genes involved in complex traits such as hypertension may be facilitated by the intermediate phenotype approach, combined with recent advances in quantitative genetics and linkage mapping. Further studies are needed to pinpoint the nature of genes in African American hypertension.

Serotonin-induced increases in platelet cytosolic calcium concentration in depressed, schizophrenic, and substance abuse patients

Exaggerated intracellular calcium responses to challenges with serotonin (5-HT) have been reported in depression. In our studies, consistent with previous reports, patients with depression exhibited an exaggerated increase in 5-HT-stimulated intracellular calcium concentration ([Ca++]i). Basal cytosolic calcium was elevated in both calcium-free and 1 mM calcium media in depressed patients. the increased responsiveness to 5-HT was seen in both conditions. Patients with schizophrenia and substance abuse did not differ from normal controls. The 5-HT response was correlated with diastolic blood pressure (r = 0.33, p = 0.02): however, this association did not fully account for the exaggerated [Ca++]i responses in the depressed group. These findings suggest that exaggerated increases in [Ca++]i in response to serotonin are a characteristic of depressed patients not shared with schizophrenic and substance abuse patients. The relationship of depression to hypertension, two conditions that share abnormalities of calcium homeostasis, warrants further study.

Na-Ca exchange in circulating blood cells

The experiments with peripheral lymphocytes raise two provocative questions: is SDCI composed of Ca influx via both a Ca channel and Na-Ca exchanger?, and what is the role of Na-Ca exchange in lymphocytes? In regard to the first issue, the potential for this dual Ca influx pathway exists, inasmuch as both Ca store depletion (by exposure of cells to EGTA) and TG-treatment initiated Ca influx that was enhanced following reversal of the Na gradient. These data could be interpreted to suggest a role for Ca influx via the exchanger during lymphocyte activation. However, our ability to demonstrate Na-Ca exchange activity was facilitated by the removal of Ca sequestering or extrusion mechanisms, including SERCA Ca pumps and forward mode Na-Ca exchange. Thus, it seems likely that under physiological conditions the primary function of the exchanger is to mediate Ca efflux. In this regard, it might play a role in lymphocyte activation by limiting net Ca entry during the sustained phase of Ca mobilization. Since sustained Ca entry is critical for Ca-dependent processes including interleukin-2 production, exchange activity would be an important modulator of this process. Changes in membrane potential, intracellular [Na] and cytosolic pH could therefore regulate Cai through its effects on Na-Ca exchange activity. Future challenges include defining the role of the Na-Ca exchange in Cai homeostasis and characterizing its function in lymphocyte populations.

Contractile responses to various inotropic agents in isolated hearts obtained from hypertensive diabetic rats

The profile of the contractile effects of calcium ions, the Ca(2+)-entry promoter Bay K 8644 and two alpha 1-adrenoceptor agonists (cirazoline and ST587) was studied in isolated perfused Langendorff hearts taken from spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) with simultaneous diabetes. In both the hypertensive and the diabetic state the isolated hearts showed a tendency to an impaired inotropic response (increase in left ventricular pressure (LVP)) towards an increase of extracellular calcium ions. The impaired inotropic response was most pronounced in hearts of rats with simultaneous diabetes and hypertension. The Ca(2+)-influx promoter Bay K 8644 did not influence the maximally developed LVP in (diabetic) SHR and WKY preparations. The inotropic responses to both cirazoline and ST587 were increased in hearts from diabetic WKY and diabetic SHR, when compared with those from control WKY and SHR. Hypertension, however, blunted the inotropic response to ST587 but not that to cirazoline when compared to hearts from control WKY or diabetic WKY. The present study indicates that the combination of hypertension and diabetes leads to progressive cardiac deterioration, likely to be the result of important changes in calcium homeostasis.

Cytosolic Ca profile of resting and thrombin-stimulated platelets from black women with NIDDM

In this study, human platelets were used as a cellular model for exploring cytosolic free Ca (Cai) regulation in non-insulin-dependent diabetes mellitus (NIDDM). Cai levels were monitored in resting and thrombin-stimulated platelets from obese females with NIDDM; obese, nondiabetic women, and nonobese, nondiabetic women. All subjects were black. Significant and marked elevation of basal Cai levels was observed in platelets from the diabetic subjects when no aspirin was used during platelet isolation. However, no significant differences were observed in Cai between aspirin-treated platelets from women with NIDDM and platelets from nondiabetic women. The rate of the Cai return to basal level after thrombin stimulation was significantly lower in platelets from the diabetic subjects, suggesting an abnormality in platelet Ca extrusion or sequestration in NIDDM. Platelet Cai levels positively correlated with low-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio (LDL/HDL) and fasting blood glucose. These findings suggest abnormalities in platelet Cai homeostasis in NIDDM that are influenced by the serum lipid profile and perhaps glucose.

Sensitivity of cardiac tissues with moderate and advanced hypertrophy to calcium ions

1. Prolonged existence of hypertension is known to induce a compensatory increase in cardiac weight, later followed by a loss of functional responsiveness to biological stimuli. 2. It was the aim of the present study to investigate the functional responses of hypertrophied hearts to rising levels of intracellular calcium. The experiments were performed using two different degrees of cardiac hypertrophy, the first as obtained in spontaneously hypertensive rats (SHR) of 18-20 weeks old, the second by using rats, 32-34 weeks old, with a surgically induced stenosis of the thoracic aorta (ASR). The ASR, which showed signs of overt heart failure, may be presented as a model for hypertension-induced end-stage cardiac hypertrophy. Age-matched normotensive Wistar-Kyoto rats (WKY) and sham-operated Wistar rats served as respective controls. 3. Different methods were employed such as increasing the extracellular Ca2+ concentration, stimulation of calcium influx by means of the calcium entry promoter Bay K 8644, or altering the sodium-calcium exchange by means of the sodium ionophore monensin. 4. The inotropic responses induced by increasing the extracellular Ca2+ concentration or provoked by the calcium entry promoter Bay K 8644 proved more pronounced in hearts taken from SHR of 18 weeks old than in those from normotensive control rats, whereas the response to monensin was found to be the same in both types of hearts. In the hearts of ASR, however, the inotropic responses to Ca2+, Bay K 8644 and monensin were strongly impaired. 5. These data demonstrate that in functional experiments the sensitivity to Ca2+, which represents the main pathway in establishing a contraction, is strongly reduced in advanced cardiac hypertrophy.

Relation of pressor responsiveness to angiotensin II and insulin resistance in hypertension

To test the hypothesis that the hypertension associated with insulin resistance is secondary to an altered responsiveness of the vasculature to pressor agents, we evaluated the relationship between insulin resistance and pressor responses to angiotensin II (AII) in 21 hypertensive (HT) and 8 normotensive (NT) subjects on both a high (200 meq) and a low (10 meq) sodium diet. When sodium balance was achieved, each supine fasting subject underwent an AII infusion at a rate of 3 ng/kg per min for 60 min, with blood pressure monitored every 2 min. On the next day under similar conditions, a euglycemic hyperinsulinemic clamp was performed, with plasma glucose clamped at 90 mg/dl for 120 min. There was no significant relationship between the glucose disposal rate (M) or the insulin sensitivity index (M divided by the mean insulin level [M/I]) and blood pressure response to AII in the NTs, but a highly significant (P < 0.019) negative correlation (r = -0.55) in the HTs. Furthermore, in eight lean HTs whose body mass index was identical to that observed in the NTs, the relationship was even more striking (P < 0.008; r = -0.85). The results on high and low salt diets were similar; however, the M and M/I were significantly increased (P < 0.05) in the NTs but not HTs with sodium restriction. In conclusion, HTs but not NTs display a striking correlation between pressor response to AII and insulin resistance. This relationship is independent of the level of sodium intake. Furthermore, sodium intake modifies insulin sensitivity in NTs but not HTs. These results strongly suggest that a primary change in pressor response to vasoactive agents in insulin-resistant subjects can contribute to their elevated blood pressure.

Preeclampsia and calcium adenosine triphosphatase activity of red blood cell ghosts

OBJECTIVE

The current work was undertaken to study the calcium adenosine triphosphatase activity of red blood cell membranes from pregnant women with preeclampsia.

STUDY DESIGN

Six normotensive and six preeclamptic pregnant women at 38 to 39 weeks of gestation were studied. The diagnosis of preeclampsia was made on the basis of blood pressure (> 140/90 mm Hg), proteinuria (> 0.5 gm of urinary protein per day), or edema. Hemoglobin-free red blood cell ghosts were prepared from the heparinized blood samples and were used to determine the calcium adenosine triphosphatase activity.

RESULTS

It was found that the calcium adenosine triphosphatase activity of preeclamptic women is diminished by about 50% compared with that of normotensive pregnant women.

CONCLUSION

A diminution of the calcium adenosine triphosphatase activity of erythrocytes in preeclampsia might be an indication that the in vivo activity of the calcium pump of these cells is diminished, which could, in turn, drive the cells to increase their cytoplasmic free calcium concentration.

Increased activity of the Mg2+/Na+ exchanger in red blood cells from essential hypertensive patients

Epidemiological, clinical, and experimental evidence suggests a relation between Mg2+ metabolism and essential hypertension. The aim of the present study was the detection of abnormalities of the erythrocyte Mg2+/Na+ exchanger in essential hypertensive patients. We studied 66 untreated essential hypertensive patients and 36 normotensive control subjects. Maximal efflux rates of total Mg2+ efflux and the Na(+)-dependent and Na(+)-independent components of Mg2+ efflux were determined in Mg(2+)-loaded red blood cells. Mg2+/Na+ exchanger was calculated as the Na(+)-dependent component of the Mg2+ efflux. Mean values of Mg2+/Na+ exchanger were clearly elevated in hypertensive subjects with respect to normotensive control subjects [184.7 +/- 15.7 versus 84.4 +/- 6 mumol(L.cell.h)-1; P < .001]. This elevation was due primarily to the increased total Mg2+ efflux [324.2 +/- 21.9 versus 257.9 +/- 17.3 mumol(L.cell.h)-1; P < .05], whereas the Na(+)-independent component was not significantly different between the groups [154.5 +/- 11.8 versus 173.4 +/- 15.5 mumol(L.cell.h)-1; P = NS]. Moreover, total erythrocyte Mg2+ content was slightly reduced in hypertensive patients with respect to normotensive control subjects (1.84 +/- 0.04 versus 2.07 +/- 0.04 mmol/L.cell; P < .001). Using the 99% confidence limits of the normotensive population as the normal range, 30 (45.5%) hypertensive subjects showed values of Mg2+/Na+ exchanger higher than 160 mumol(L.cell.h)-1. The Mg2+/Na+ exchanger was inversely correlated with basal intraerythrocyte Mg2+ content (r = -.323; P = .001). From a clinical point of view, we found a positive correlation between diastolic blood pressure values and Mg2+/Na+ exchanger (r = .246; P < .05) in the sample of essential hypertensive patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood pressure inversely correlates with thrombin-evoked calcium rise in platelets

Earlier investigations showed a positive correlation between basal cytosolic free calcium in human platelets and blood pressure; however, recent studies have failed to show this relation. We undertook the present work to examine which platelet cytosolic calcium parameters (namely, cytosolic calcium in resting or stimulated states in calcium-containing and calcium-free media) present the least variability and best correlation with blood pressure. We studied 17 healthy white men on three different occasions separated by 1- and 4-week intervals. Their manual and ambulatory automated 24-hour blood pressure measurements were correlated with cytosolic calcium in resting and stimulated (thrombin-treated) fura 2-loaded platelets. The following cytosolic calcium parameters were measured in 1 mmol/L calcium and calcium-free media: basal cytosolic calcium, peak thrombin-evoked cytosolic calcium, and post-transient cytosolic calcium 5 minutes after thrombin treatment. The highest and lowest coefficients of variation were respectively shown by the basal cytosolic calcium (22.8%) and peak thrombin-evoked cytosolic calcium (10.1%) in calcium medium. Basal cytosolic calcium did not correlate with any of the blood pressure parameters. Of the cytosolic calcium parameters, peak thrombin-evoked cytosolic calcium in calcium medium demonstrated consistent (negative) correlations with blood pressure, with better correlations shown with diastolic than systolic blood pressure of both automated and manual blood pressure readings. Peak thrombin-evoked cytosolic calcium in calcium medium showed similar correlations with nighttime and daytime automated blood pressure measurements. There were no correlations between peak thrombin-evoked cytosolic calcium in calcium-free medium and blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular calcium concentration and activation of the Na+/H+ exchanger in essential hypertension

To investigate the relationship between changes in intracellular calcium concentration ([Ca2+]i) and agonist-induced activation of the Na+/H+ exchanger in essential hypertension (EH), platelet [Ca2+]i and pHi were measured in 24 patients with EH (14 males) aged 48 +/- 2 years and 23 matched normotensive controls (NT) (12 males) aged 45 +/- 3 years. Measurements were done with spectrofluorimetry using the dyes Fura-2 for [Ca2+]i and BCECF for pHi. [Ca2+]i and pHi were measured in the resting condition and after stimulation in vitro with 0.1 U/ml human thrombin. The thrombin-induced rise in pHi was Na+ dependent and amiloride sensitive, indicating that it was mediated by the Na+/H+ exchanger. Unstimulated [Ca2+]i was higher in patients with EH than in NT (60 +/- 3 vs. 48 +/- 1 nmol/liter, P < 0.005), but there were no differences in resting pHi between both groups (7.16 +/- 0.01 vs. 7.16 +/- 0.008). In the presence of 1 mmol/liter external calcium (Ca2+o), thrombin-induced increment in [Ca2+]i was significantly greater in patients with EH than in NT (281 +/- 21 vs. 206 +/- 19; P < 0.05) as was the pHi increment (EH: 0.137 +/- 0.01; NT: 0.095 +/- 0.01; P < 0.05). Both agonist-induced increments in [Ca2+]i and in pHi were correlated with mean arterial pressure (MAP) only in the EH group (r = 0.58, P < 0.005 and r = 0.59, P < 0.005, respectively). The agonist-induced rise in pHi was positively correlated with the rise in [Ca2+]i both in the EH group (r = 0.65, P < 0.001) and in the NT (r = 0.55, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations of membrane properties in erythrocytes of salt hypertensive Sabra rats

This study was designed to investigate the effects of a hypertensive stimulus, high salt intake, in hypertension-prone (SBH) and -resistant (SBN) Sabra rats on erythrocyte Na+ content (Na+i), Ca2+ influx and cytosolic Ca2+ concentration ([Ca2+]i). The relationships of these parameters to plasma lipids, circulating digoxin-like immunoreactivity and membrane microviscosity, determined by the fluorescence anisotropy of trimethylamino-diphenylhexatriene (TMA-DPH) and diphenylhexatriene (DPH), were also evaluated. Erythrocytes of SBH rats were characterized by increased [Ca2+]i, unchanged Ca2+ influx and reduced Na+i. There were no significant differences in the plasma digoxin-like immunoreactivity between the two strains. High-salt intake decreased membrane microviscosity (DPH anisotropy) in SBH rats but did not alter the above parameters. Erythrocyte [Ca2+]i correlated positively with diastolic blood pressure and negatively with erythrocyte Na+i. Membrane dynamics evaluated by the two fluorescent probes did not correlate with [Ca2+]i, Ca2+ influx or Na+i whereas DPH anisotropy was inversely related to blood pressure. These relationships were independent of plasma cholesterol or triglycerides. It can be concluded that 1) similarly to earlier observations in essential hypertension and spontaneously hypertensive rats, erythrocyte [Ca2+]i correlates positively with blood pressure in salt-dependent hypertension, and 2) increased erythrocyte Na+ content need not be a hallmark of hypertension.

Effects of weight reduction on cellular cation metabolism and vascular resistance

The early stages of weight loss are associated with a reduction in blood pressure, and the mechanisms mediating this reduction remain unclear. Platelet free calcium levels, [Ca2+]i, have been reported to be elevated in essential hypertension and to decrease with pharmacological treatment of the hypertension. In the current study, 18 obese subjects had measurements of blood pressure, forearm blood flow, forearm vascular resistance, and both basal platelet [Ca2+]i and [Ca2+]i responses to vasopressin during 12 weeks on a very low calorie (3,360 kJ, or 800 kcal) diet. Weight reduction was associated with reduction in mean arterial blood pressure at 3-4 weeks. There were associated reductions in forearm vascular resistance and platelet [Ca2+]i as well as increases in forearm blood flow at 3-4 weeks of the diet. Increased forearm blood flow was correlated with weight loss. Vasopressin-induced platelet [Ca2+]i responses increased, which correlated with the reduction in mean arterial pressure at 7-8 weeks of weight loss. Assuming that platelet [Ca2+]i metabolism reflects vascular smooth muscle cell [Ca2+]i metabolism, the data suggest that blood pressure reduction after weight loss may be related to reduced vascular smooth muscle cell [Ca2+]i. The reason for the increased vasopressin-induced [Ca2+]i after weight reduction is unclear.

Platelet sodium-hydrogen antiport in obese and diabetic black women

In this investigation we correlated platelet Na-H antiport parameters with blood pressure and serum lipids in a sample population of non-insulin-dependent diabetic obese, nondiabetic obese, and nondiabetic nonobese black women. Parameters of the Na-H antiport were examined in aspirin-treated platelets. These parameters were not altered in resting or in thrombin-stimulated platelets of diabetic patients. The activity index of platelet Na-H antiport after thrombin stimulation was positively correlated with the blood pressure (systolic blood pressure, r = 0.5320 and p = 0.0001; diastolic blood pressure, r = 0.5123 and p = 0.0017). Lower high density lipoprotein cholesterol levels were associated with an alkaline shift in the cytosolic pH set point for activation of the Na-H antiport. Highly significant correlations were also observed between the total cholesterol/high density lipoprotein cholesterol ratio and the cytosolic pH set point for activation of the Na-H antiport. These correlations were independent of diabetes or the body mass index. Together, these observations indicate that parameters of platelet Na-H antiport are altered with an increase in blood pressure and a decrease in serum high density lipoprotein cholesterol.

Hypotensive drugs and the cellular energetic potential

Clinical and experimental investigations have revealed changes of the Na, K, Ca and Mg concentration in serum and cells in patients with essential arterial hypertension (EAH). Some hypotensive drugs correct, more or less, the electrolytic abnormalities at the same time as the decrease of arterial pressure. Epidemiological studies have shown a lower arterial blood pressure in populations with decreased intake of Na and an increased intake of K, Ca and Mg. However the most frequently encountered electrolyte anomaly in patients with EAH is hypophosphatemia, mainly induced by a shift of inorganic phosphate from serum into the cells. Probably the increased influx of inorganic phosphate from the serum, increases the arterial cellular energetic potential. As hypotensive drugs lead to a reduction of the inorganic phosphate shift from serum into the cells one may suggest that the obtained decrease of arterial blood pressure may be at least partially due to a diminished energetic potential of certain cells.

Disturbed calcium metabolism in offspring of hypertensive parents

To assess a possible heritability of a disturbed calcium metabolism in relation to blood pressure regulation, 28 young normotensive offspring of either hypertensive or normotensive parents were studied while administered a defined diet with daily sodium chloride of 6 and 20 g/day for 7 days each. Before the high salt diet was begun, the cytosolic calcium concentration ([Ca2+]i) in platelets was elevated in offspring of hypertensive parents, whereas serum electrolytes, plasma renin activity, plasma catecholamines, and 24-hour urinary excretion of sodium and calcium showed no difference between the two groups. On exposure to a high salt diet, the mean blood pressure increased (from 80 +/- 2 to 85 +/- 2 mm Hg, p less than 0.05) in offspring of hypertensive parents. These changes in mean blood pressure were positively correlated with the basal platelet [Ca2+]i (r = 0.61, p less than 0.01), whereas [Ca2+]i did not demonstrate any significant changes. When the subjects were administered the high salt diet, plasma ionized calcium decreased (from 2.37 to 2.21 meq/l, p less than 0.05) and 1,25-dihydroxyvitamin D3 increased (from 32.7 to 40.8 pg/ml, p less than 0.05) with a transient relative hypercalciuria in offspring of hypertensive parents. This increase of 1,25-dihydroxyvitamin D3 was significantly correlated with the changes in mean blood pressure (r = 0.62, p less than 0.01). Disturbed intraplatelet and systemic calcium metabolism may be of predictive value in the development of hypertension.

Cyclic nucleotides attenuate thrombin-evoked alterations in parameters of platelet Na/H antiport. The role of cytosolic Ca

In this work, we explored the role of cyclic nucleotides in modulating parameters of the Na/H antiport in human platelets. Sodium nitroprusside and iloprost, as well as cyclic nucleotide analogues, were used to raise cellular levels of cAMP and cGMP. Cyclic nucleotides reversed the thrombin-evoked alkaline shift in cytosolic pH set point and the activity of the Na/H antiport, concurrently with attenuation of thrombin-induced rise in cytosolic free Ca. No effect of cyclic nucleotides was observed in platelets not treated with thrombin, or platelets subjected to phorbol 12-myristate 13-acetate. cAMP did not reverse ionomycin-induced changes in the parameters of the Na/H antiport. Collectively, these observations indicate that cyclic nucleotides modulate the Na/H antiporter in human platelets through their effect on thrombin-evoked changes in cytosolic free Ca. Presumably, this effect holds for other agonists which stimulate phospholipase C, raise cytosolic-free Ca, and activate the Na/H antiport through protein kinase C dependent and protein kinase C-independent mechanisms.

Magnesium supplementation prevents the development of alcohol-induced hypertension

The effect of chronic alcohol administration on blood pressure was investigated in 7-week-old Wistar rats. Tail-cuff blood pressure was significantly higher in rats who received 15% ethanol in drinking water than in control rats. Intracellular free calcium concentration of lymphocytes was increased, while magnesium concentration of erythrocyte, aorta, and skeletal muscle and erythrocyte ouabain-sensitive 22Na efflux rate constant (Kos) were decreased in alcohol-induced hypertensive rats but not in control rats. Extracellular fluid volume was also increased in alcohol-administered rats. Oral magnesium supplementation (1% MgO in rat chow) attenuated the development of alcohol-induced hypertension accompanied by increased magnesium concentration of erythrocyte, aorta, skeletal muscle, and Kos and decreased intraerythrocyte sodium concentration. Norepinephrine half-life time of the heart and spleen was also increased in magnesium-supplemented rats. Blood pressure significantly correlated positively with intracellular calcium concentration and extracellular fluid volume, negatively with magnesium concentration of erythrocyte, aorta, skeletal muscle, and Kos. These results suggest that increased intracellular calcium, which was partly due to magnesium depletion and suppressed sodium pump activity, and expanded body fluid volume had a possible role in the development of alcohol-induced hypertension. It is also suggested that oral magnesium supplementation had a hypotensive effect on alcohol-induced hypertension possibly through decreased intracellular sodium concentration caused by an activation of sodium pump and decreased sympathetic nervous activity.

Mild exercise decreases plasma endogenous digitalislike substance in hypertensive individuals

Changes in a plasma endogenous digitalislike substance were investigated in relation to the antihypertensive mechanism of mild exercise. Fifteen women with mild essential hypertension and seven normotensive female volunteers were divided into exercised hypertensive (n = 10), nonexercised hypertensive (n = 5), and nonexercised normotensive (n = 7) groups. A 4-week general clinical observation period preceded the study period of 10 weeks. The exercised hypertensive individuals were treated with a lactate threshold exercise that corresponded to approximately 50% of the maximum oxygen consumption three times a week, whereas the nonexercised groups were observed at the outpatient clinic as control groups. In the exercised group, systolic blood pressure fell by 7 mm Hg (p = 0.05), diastolic by 6 mm Hg (p less than 0.01), and mean blood pressure by 7 mm Hg (p less than 0.01) after 10 weeks. The reduction in the plasma endogenous digitalislike substance was significant after 7 (-1.02 ng/ml, p less than 0.05) and 10 (-1.04 ng/ml, p less than 0.05) weeks in this group. It positively correlated with the reduction in diastolic (r = 0.70, p less than 0.05) or mean (r = 0.66, p less than 0.05) blood pressure and with changes in plasma norepinephrine (r = 0.76, p less than 0.05). The mean corpuscular volume of erythrocytes decreased (-1.7 fl, p less than 0.01) after 10 weeks of exercise, and the plasma volume index tended to decrease (-108 ml/m2, p = 0.28). In the control groups, significant changes in blood pressure and plasma endogenous digitalislike substance were not observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Rise and fall of agonist-evoked platelet Ca2+ in hypertensive rats

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.

Role of platelet cytosolic calcium in the response to salt intake in normotensive subjects

1. To investigate the role of cytosolic calcium in salt-induced hypertension, a high salt diet was given to young normotensive subjects with or without a family history of hypertension. 2. A high salt diet raised blood pressure significantly in normotensive subjects with a family history compared with the age and gender matched subjects without a predisposition to hypertension. 3. Platelet cytosolic calcium was increased in predisposed subjects in a control period before salt intake. 4. A positive correlation was observed between the changes in mean blood pressure and cytosolic calcium before high salt intake, although salt loading did not induce any significant change in cytosolic calcium. 5. These results suggest that cytosolic calcium plays a role in elevation of blood pressure induced by salt loading in subjects with a family history of hypertension.

Parathyroid hormone, platelet calcium, and blood pressure in normotensive subjects

Relations between platelet cytosolic calcium, parathyroid hormone, and blood pressure were investigated in 91 normotensive subjects: 47 men and 44 women ranging in age from 24 to 70 years. The men had higher mean arterial blood pressure, serum creatinine, and body mass index than the women. Serum total calcium, plasma ionized calcium, and parathyroid hormone (measured as both intact hormone and mid-molecule fragment) were not different between men and women; however, serum phosphate was higher in women than in men. Basal platelet cytosolic calcium was higher in men than in women (113.7 +/- 1.9 versus 105.9 +/- 1.7, respectively; p less than 0.01), but there was no difference in the peak platelet cytosolic calcium responses to thrombin between the two groups. In the combined group of male and female subjects, platelet cytosolic calcium correlated with diastolic blood pressure and mean arterial pressure (r = 0.37, p less than 0.001 and r = 0.32, p less than 0.01, respectively). Intact parathyroid hormone correlated with systolic and mean arterial blood pressure (r = 0.41, p less than 0.001 for both). Age correlated with both systolic blood pressure (r = 0.40, p less than 0.001) and intact parathyroid hormone (r = 0.51, p less than 0.001). When multiple regression analysis was performed using mean arterial pressure as the dependent variable, platelet cytosolic calcium and intact parathyroid hormone maintained significant correlations with mean arterial pressure. Platelet cytosolic calcium did not correlate with intact parathyroid hormone. These results suggest that both platelet cytosolic calcium and intact parathyroid hormone are associated with blood pressure regulation in normotensive subjects. However, the influences of these two factors on blood pressure are not interrelated.

Effect of coenzyme Q10 on structural alterations in the renal membrane of stroke-prone spontaneously hypertensive rats

To test the hypothesis that structural abnormalities exist in the kidney membrane of spontaneously hypertensive rats, we examined the effect of long-term administration of coenzyme Q10 on membrane lipid alterations in the kidney of stroke-prone spontaneously hypertensive rats (SHRSP). As compared with normotensive Wistar-Kyoto rats, renal membrane phospholipids, especially phosphatidylcholine and phosphatidylethanolamine, decreased and renal phospholipase A2 activity was enhanced with age in untreated SHRSP. Treatment with coenzyme Q10 attenuated the elevation of blood pressure, the membranous phospholipid degradation, and the enhanced phospholipase A2 activity. These results suggest that one factor contributing to the progress of hypertension is a structural membrane abnormality that alters the physical and functional properties of the cell membrane, and coenzyme Q10 might protect the renal membrane from damage due to hypertension in SHRSP.

Modifications induced by gestational hypertension on platelet calcium transport

Several studies have recently demonstrated that the platelets of subjects affected by essential hypertension have, in their basal state, an elevated cellular calcium content. Such data appear particularly interesting with regard to gestational hypertension (GH). Supposing that the intracellular calcium may be involved in the regulation of blood pressure we have studied the cytosolic calcium concentration, Na+/K(+)-ATPase activity, Ca(2+)-ATPase activity, fluidity, and the cholesterol/phospholipid (C/P) molar ratio of the plasma membranes in platelets from 20 normotensive pregnant women and 20 women affected by mild gestational hypertension without pharmacological treatment, near term. We observed an increased Ca(2+)-ATPase activity and a decreased Na(+)K(+)-ATPase activity in GH compared to the controls, accompanied by an increased Ca2+ intraplatelet concentration in the same patients. The fluidity and the C/P molar ratio were also increased. Our study gives indirect support to the hypothesis, supposing a reduced Na+/K(+)-ATPase activity which might cause increased intracellular Na+ content and decreased Ca2+ efflux through the Na+/Ca2+ exchange. However, out data can not rule out the other hypotheses explaining the increased cellular Ca2+ content. The present data indicate that GH is accompanied by a membrane structural abnormality that alters its physical state and modifies the membrane-related cellular functions.

Effect of weight reduction in moderately overweight patients on recorded ambulatory blood pressure and free cytosolic platelet calcium

Although platelet cytosolic calcium has been shown to decrease during pharmacological treatment of hypertension, there is no evidence that cytosolic calcium also falls during a nonpharmacological reduction in blood pressure. To provide such evidence, we examined prospectively the relation between platelet cytosolic calcium and ambulatory blood pressure during weight reduction in moderately overweight (body mass index [BMI] greater than 25), mildly hypertensive individuals. The experimental group (responders: BMI reduction greater than 5%) consisted of 19 patients who lost 8.5 +/- 2.9 kg (mean +/- SD, p less than 0.05) during a 10-week hypocaloric diet, whereas the control group (nonresponders: BMI reduction less than 5%) consisted of 12 patients who showed no relevant change in body weight (-2.0 +/- 1.3 kg) during the same period of time. The moderate weight loss of the responders decreased blood pressure by 14/5 mm Hg (p less than 0.05), as measured by ambulatory monitoring, which renders a placebo effect unlikely. This nonpharmacological reduction in blood pressure was accompanied by a proportional 11% decrease (p less than 0.05) in platelet cytosolic calcium and also by significant (p less than 0.05) decreases in plasma catecholamines and serum cholesterol. These findings establish the concept of a nonpharmacological reduction in free cytosolic platelet calcium in humans and add further evidence suggesting a link between intracellular calcium homeostasis and blood pressure regulation.