Abnormal platelet and lymphocyte calcium handling in prehypertensive rats

Moringa oleifera-rich diet and T cell calcium signaling in spontaneously hypertensive rats

Moringa oleifera is a plant whose fruits, roots and leaves have been advocated for traditional medicinal uses. The physicochemical analysis shows that Moringa oleifera contains more dietary polyunsaturated fatty acids (PUFA) than saturated fatty acids (SFA). The consumption of an experimental diet enriched with Moringa oleifera extracts lowered blood pressure in spontaneously hypertensive rats (SHR), but not in normotensive Wistar-Kyoto (WKY) rats as compared to rats fed an unsupplemented control diet. Anti-CD3-stimulated T cell proliferation was diminished in both strains of rats fed the Moringa oleifera. The experimental diet lowered secretion of interleukin-2 in SHR, but not in WKY rats compared with rats fed the control diet. Studies of platelets from patients with primary hypertension and from SHR support the notion that the concentration of intracellular free calcium [Ca(2+)](i) is modified in both clinical and experimental hypertension. We observed that the basal, [Ca(2+)](i) was lower in T cells of SHR than in those of WKY rats fed the control diet. Feeding the diet with Moringa oleifera extracts to WKY rats did not alter basal [Ca(2+)](i) in T cells but increased basal [Ca(2+)](i) in SHR. Our study clearly demonstrated that Moringa oleifera exerts antihypertensive effects by inhibiting the secretion of IL-2 and modulates T cell calcium signaling in hypertensive rats.

Effect of roscovitine on intracellular calcium dynamics: differential enantioselective responses

Cyclin-dependent kinases (CDKs) inhibitors have emerged as interesting therapeutic candidates. Of these, (S)-roscovitine has been proposed as potential neuroprotective molecule for stroke while (R)-roscovitine is currently entering phase II clinical trials against cancers and phase I clinical tests against glomerulonephritis. In addition, (R)-roscovitine has been suggested as potential antihypertensive and anti-inflammatory drug. Dysfunction of intracellular calcium balance is a common denominator of these diseases, and the two roscovitine enantiomers (S and R) are known to modulate calcium voltage channel activity differentially. Here, we provide a detailed description of short- and long-term responses of roscovitine on intracellular calcium handling in renal epithelial cells. Short-term exposure to (S)-roscovitine induced a cytosolic calcium peak, which was abolished after stores depletion with cyclopiazonic acid (CPA). Instead, (R)-roscovitine caused a calcium peak followed by a small calcium plateau. Cytosolic calcium response was prevented after stores depletion. Bafilomycin, a selective vacuolar H(+)-ATPase inhibitor, abolished the small calcium plateau. Long-term exposure to (R)-roscovitine significantly reduced the basal calcium level compared to control and (S)-roscovitine treated cells. However, both enantiomers increased calcium accumulation in the endoplasmic reticulum (ER). Consistently, cells treated with (R)-roscovitine showed a significant increase in SERCA activity, whereas (S)-roscovitine incubation resulted in a reduced PMCA expression. We also found a tonic decreased ability to release calcium from the ER, likely via IP3 signaling, under treatment with (S)- or (R)-roscovitine. Together our data revealed that (S)-roscovitine and (R)-roscovitine exert distinct enantiospecific effects on intracellular calcium signaling in renal epithelial cells. This distinct pharmacological profile can be relevant for roscovitine clinical use.

Overview of animal models of attention deficit hyperactivity disorder (ADHD)

Attention-deficit/hyperactivity disorder (ADHD) is a heterogeneous, highly heritable, behavioral disorder that affects ∼5% to 10% of children worldwide. Although animal models cannot truly reflect human psychiatric disorders, they can provide insight into the disorder that cannot be obtained from human studies because of the limitations of available techniques. Genetic models include the spontaneously hypertensive rat (SHR), the Naples High Excitability (NHE) rat, poor performers in the 5-choice serial reaction time (5-CSRT) task, the dopamine transporter (DAT) knock-out mouse, the SNAP-25 deficient mutant coloboma mouse, mice expressing a human mutant thyroid hormone receptor, a nicotinic receptor knock-out mouse, and a tachykinin-1 (NK1) receptor knock-out mouse. Chemically induced models of ADHD include prenatal or early postnatal exposure to ethanol, nicotine, polychlorinated biphenyls, or 6-hydroxydopamine (6-OHDA). Environmentally induced models have also been suggested; these include neonatal anoxia and rat pups reared in social isolation. The major insight provided by animal models was the consistency of findings regarding the involvement of dopaminergic, noradrenergic, and sometimes also serotonergic systems, as well as more fundamental defects in neurotransmission.

Increased transient receptor potential canonical type 3 channels in vasculature from hypertensive rats

We tested the hypothesis that transient receptor potential canonical type 3 (TRPC3) channels are increased in vascular smooth muscle cells and aortic tissue from spontaneously hypertensive rats (SHR) compared with normotensive Wistar Kyoto rats. Expression of TRPC3 was analyzed by immunohistochemistry and Western blotting. TRPC3 gene knockdown was performed by specific small interfering RNA and TRPC3 overexpression using the pAdEasy-1 system. Cytosolic calcium was measured using fluorescence spectrophotometry and vasoconstriction of aortic rings using a force transducer. In SHR, the expression of TRPC3 channel protein was significantly higher in aortic rings (1.48+/-0.05 versus 1.00+/-0.06; each n=6; P<0.01) and vascular smooth muscle cells (1.28+/-0.08 versus 1.00+/-0.03; each n=6; P<0.05) compared with Wistar Kyoto rats. Knockdown of TRPC3 gene expression by specific small interfering RNA significantly reduced the angiotensin II-induced calcium influx by 30+/-3% (n=6; P<0.01), whereas TRPC3 overexpression significantly increased it by 55+/-3% (n=6; P<0.01). The angiotensin II-induced calcium increase was significantly enhanced in vascular smooth muscle cells from SHR compared with Wistar Kyoto rats, even in the presence of the calcium channel blocker amlodipine. Angiotensin II significantly elevated the TRPC3 channel protein expression in vascular smooth muscle cells from SHR from 1.28+/-0.08 to 1.61+/-0.08 (each n=6; P<0.01). Angiotensin II-induced TRPC3 expression was prevented by telmisartan. Administration of telmisartan to SHR for 4 weeks significantly reduced blood pressure, angiotensin II-induced vasoconstriction, and TRPC3 channel protein expression in aortic tissue. TRPC3 expression was not significantly reduced after reduction of blood pressure in SHR using amlodipine. In conclusion, we give experimental evidence that increased TRPC3 channel protein expression in the vasculature is important for elevated blood pressure.

Neurobiology of animal models of attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a heterogeneous, highly heritable, disorder resulting from complex gene-gene and gene-environment interactions. The defining symptoms of hyperactivity, impulsivity and impaired sustained attention are not unique to ADHD. It is therefore not surprising that animals with distinctly different neural defects model the behavioural characteristics of the disorder. Consistent with ADHD being a developmental disorder, animal models are either genetic (spontaneously hypertensive rats (SHR), dopamine transporter (DAT) knock-out mice, SNAP-25 mutant mice, mice expressing a mutant thyroid receptor) or have suffered an insult to the central nervous system during the early stages of development (anoxia, 6-hydroxydopamine). It appears that neural transmission is impaired by either direct disruption of dopaminergic transmission or a more general impairment of neurotransmission that gives rise to compensatory changes in monoaminergic systems that are not sufficient to completely normalize neural function. In general, results obtained with animal studies suggest that dopamine neurons are functionally impaired. However, evidence obtained from some animal models suggests that the noradrenergic and serotonergic neurotransmitter systems may be the target of drugs that ameliorate ADHD symptoms.

Effect of amlodipine and cilazapril treatment on platelet Ca2+ handling in spontaneously hypertensive rats

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.

Salt-loading elevates blood pressure and aggravates insulin resistance in Wistar fatty rats: a possible role for enhanced Na+ -H+ exchanger activity

OBJECTIVE

Increased Na+-H+ exchanger activity (NHE) has been reported as an intermediate phenotype in hypertensive subjects, particularly those with insulin resistance. To investigate whether NHE abnormality plays a role in hypertension, Wistar fatty rat (WFR) with overt obesity, hyperglycemia and marked hyperinsulinemia was examined.

METHODS

WFR and Wistar lean rats (WLR) as a control (n = 12, each) were fed either with normal (0.38%) or high sodium (4% NaCl) diet for 12 weeks and then sacrificed to examine platelets NHE activity.

RESULTS

Mean arterial pressure (MAP) was higher in WFR than in WLR (113 +/- 4 versus 96 +/- 7 mmHg, P < 0.05) under a normal chow. Vmax values of NHE activity were significantly higher in WFR than in WLR. WFR fed with a high sodium diet showed higher MAP than those with a normal chow (128 +/- 3 versus 113 +/- 4 mmHg, P < 0.05). Though Km values were not different between WFR and WLR under a normal chow, both maximal transport rate (Vmax) and half maximal transport (Km) values were significantly higher in WFR with a high salt diet than those with a control diet. Vmax showed significant correlation with MAP, whereas Km values correlated with immunoreactive insulin (IRI) levels. Significant interaction between dietary sodium intake and the strain differences was observed both on blood pressure and on IRI levels by two-way analysis of variance (ANOVA).

CONCLUSION

WFR presented salt-sensitive blood pressure elevation. NHE activity was enhanced in WFR in correlation with the blood pressure. These results suggest that augmented NHE activity contributes to the development of salt-sensitive blood pressure elevation in WFR.

Resetting of the cardiopulmonary baroreflex 10 years after surgical repair of coarctation of the aorta

OBJECTIVE

To characterise cardiopulmonary baroreflex responses and examine the effects of a 45 minute cycling bout late after successful repair of coarctation of the aorta.

SUBJECTS

10 young adults (mean (SEM) age 18.1 (2.6 years)) operated on for coarctation of the aorta 12.7 (3.5) years earlier, and 10 healthy controls.

DESIGN

Forearm blood flow (venous occlusion plethysmography) and vascular resistance, left ventricular internal diastolic diameter, and central venous pressure estimated from an antecubital vein were measured in the supine position at baseline and during five minute applications of lower body negative pressure (LBNP) at -15 mm Hg (LBNP(-15)) and -40 mm Hg (LBNP(-40)). Venous samples were obtained at baseline and during LBNP(-40) for noradrenaline (norepinephrine), adrenaline (epinephrine), renin activity, and aldosterone. The tests were repeated after 45 minutes of moderate exercise.

RESULTS

Baseline heart rate (78 (9) v 64 (6) beats/min), echocardiographic cardiac output (6.9 (1.1) v 5.0 (0.2) l/min), shortening fraction (41.7 (1.8)% v 33.3 (1.3)%), and forearm blood flow (3.4 (0.4) v 2.3 (0.3) ml/100 g/min) were higher in the coarctation group than in the controls (p < 0.05). Changes in forearm blood flow and forearm vascular resistance from baseline to LBNP(-40) were similar in both groups, but the relation between forearm vascular resistance and estimated central venous pressure or left ventricular internal diastolic diameter was shifted downward in the coarctation group. Plasma adrenaline was increased in the coarctation group (baseline: 3.2 (0.6) v 2.4 (0.3) pmol/l in controls; LBNP(-40): 687 (151) v 332 (42) pmol/l) (p < 0.05). Both groups showed a similar downward displacement of forearm vascular resistance (p < 0.05) after exercise.

CONCLUSIONS

There appears to be resetting of the cardiopulmonary baroreflex to a lower forearm vascular resistance in young adults operated on for coarctation of the aorta, associated with hyperdynamic left ventricular function. Raised circulating adrenaline could contribute to the lower forearm vascular resistance.

Expression of Ca(2+) Transport Genes in Platelets and Endothelial Cells in Hypertension

-Altered Ca(2+) handling is observed in different cells in essential hypertension. We investigated the expression of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) and inositol 1,4,5-trisphosphate receptor (IP(3)R) isoforms in platelets and aortic endothelial cells (EC) isolated from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats by ratio reverse-transcriptase-polymerase chain reaction (RT-PCR) analysis and Western blotting. SERCA2b and SERCA3 were assessed at mRNA (EC and platelets) and at protein level (platelets). IP(3)R1, IP(3)R2, and IP(3)R3 mRNAs were demonstrated in both cell types, but only IP(3)R1 and IP(3)R2 proteins were detected in platelets. Compared with WKY, SHR EC and platelets showed higher SERCA3 and IP(3)R2 expression and lower IP(3)R1 expression. We then investigated the effect of lisinopril (20 mg. kg(-)(1). d(-)(1); 10-week treatment of 4-week-old rats or 2-week treatment of adult rats) and captopril (100 mg. kg(-)(1). d(-)(1); 2-week treatment of adult rats). Consequently, expression patterns of SERCAs and IP(3)Rs were significantly modified. Except for SERCAs mRNA in platelets, all differences between SHR and WKY disappeared. However, SERCA3 remained the predominant isoform. Both EC and platelets demonstrated a high equal expression of IP(3)R2 mRNA. IP(3)R1 was the predominant platelet protein isoform, as it was in untreated WKY. mRNA was also isolated from pancreatic islets of WKY and SHR, but no effect of either rat strain or of lisinopril treatment was observed on the expression of the studied genes. We hypothesize that the identical expression pattern of SERCAs and IP(3)Rs after treatment with ACE inhibitors represents a different nonhypertensive configuration, which, through changes in intracellular Ca(2+) handling, improves endothelial and platelet dysfunction in SHR but has no effect in WKY.

Abnormal intracellular ca(2+)homeostasis and disease

A whole range of cell functions are regulated by the free cytosolic Ca(2+)concentration. Activator Ca(2+)from the extracellular space enters the cell through various types of Ca(2+)channels and sometimes the Na(+)/Ca(2+)-exchanger, and is actively extruded from the cell by Ca(2+)pumps and Na(+)/Ca(2+)-exchangers. Activator Ca(2+)can also be released from internal Ca(2+)stores through inositol trisphosphate or ryanodine receptors and is taken up into these organelles by means of Ca(2+)pumps. The resulting Ca(2+)signal is highly organized in space, frequency and amplitude because the localization and the integrated free cytosolic Ca(2+)concentration over time contain specific information. Mutations or functional abnormalities in the various Ca(2+)transporters, which in vitro seem to induce trivial functional alterations, therefore, often lead to a plethora of diseases. Skeletal-muscle pathology can be caused by mutations in ryanodine receptors (malignant hyperthermia, porcine stress syndrome, central-core disease), dihydropyridine receptors (familial hypokalemic periodic paralysis, malignant hyperthermia, muscular dysgenesis) or Ca(2+)pumps (Brody disease). Ca(2+)-pump mutations in cutaneous epidermal keratinocytes and cochlear hair cells lead to, skin diseases (Darier and Hailey-Hailey) and hearing/vestibular problems respectively. Mutated Ca(2+)channels in the photoreceptor plasma membrane cause vision problems. Hemiplegic migraine, spinocerebellar ataxia type-6, one form of episodic ataxia and some forms of epilepsy can be due to mutations in plasma-membrane Ca(2+)channels, while antibodies against these channels play a pathogenic role in all patients with the Lambert-Eaton myasthenic syndrome and may be of significance in sporadic amyotrophic lateral sclerosis. Brain inositol trisphosphate receptors have been hypothesized to contribute to the pathology in opisthotonos mice, manic-depressive illness and perhaps Alzheimer's disease. Various abnormalities in Ca(2+)-handling proteins have been described in heart during aging, hypertrophy, heart failure and during treatment with immunosuppressive drugs and in diabetes mellitus. In some instances, disease-causing mutations or abnormalities provide us with new insights into the cell biology of the various Ca(2+)transporters.

Platelet Ca(2+)ATPases : a plural, species-specific, and multiple hypertension-regulated expression system

Gaining insight into nonmuscle Ca(2+) signaling requires basic knowledge of the major structures involved. We investigated the expression of platelet Ca(2+)ATPases in normal and hypertension-associated abnormal Ca(2+) signaling. First, overall identification of normotensive Wistar-Kyoto rat Ca(2+)ATPases was attempted by looking for newly described human platelet 3'-end alternatively spliced sarco/endoplasmic reticulum Ca(2+)ATPases (SERCA) 3b mRNA and plasma membrane Ca(2+)ATPase (PMCA) 1b and 4b proteins, in addition to SERCA2b and SERCA3a isoforms. For SERCAs, comparative analyses of human and Wistar-Kyoto rat SERCA3 platelet mRNA by reverse transcription-polymerase chain reaction (RT-PCR) followed by sequencing established that human platelets coexpressed SERCA3b and a third SERCA3c, while rat cells were devoid of them but expressed a still unknown splice variant that we termed rSERCA3b/3c. Its identification using 3'-end SERCA3 gene and rapid amplification of cDNA ends (RACE)-PCR studies showed that it results from an additional SERCA3 alternative splicing process, which uses a second alternative polyadenylation site located in the last intron. For PMCAs, with the use of gene-specific RT-PCR followed by sequencing and Western blotting using 5F10 monoclonal antibody, expression of human and rat platelet PMCA1b and PMCA4b was similar. Second, comparative analysis of these newly identified Ca(2+)ATPases and SERCA3a in age-matched spontaneously hypertensive rat platelets demonstrated (1) a marked downregulation of rSERCA3b/3c, which became null, and a 1.71-fold increase in SERCA3a and (2) an opposite regulation of the 2 PMCAs, namely, a 3.3-fold decrease in PMCA1b mRNA and a 3.7-fold increase in PMCA4b mRNA. Hence, platelets coexpress multiple, diverse, and species-specific Ca(2+)ATPases, including a novel fourth SERCA3. Moreover, expression of PMCA (1b and 4b), SERCA3a, and rSERCA3b/3c was modulated in rat hypertension. Hence, Ca(2+)ATPases should be regarded as constituting a new rational basis for the understanding of nonmuscle cell Ca(2+) signaling.

Abnormal platelet Ca2+ handling accompanied by increased cytosolic free Mg2+ in essential hypertension

To test the hypothesis that abnormal platelet Ca2+ handling in essential hypertension results from cellular Mg2+ deficiency, cytosolic free Mg2+ concentration ([Mg2+]i) and Ca2+ metabolism were studied in mag-fura 2 and fura 2-loaded platelets from 30 essential hypertensive patients and 30 sex- and age-matched normotensive controls. Basal cytosolic free Ca2+ concentration ([Ca2+]i) and intracellular Ca2+ discharge capacity were higher in hypertensives than in normotensives (22 +/- 5 vs. 18 +/- 5 nM, P < 0.05; 743 +/- 250 vs. 624 +/- 144 nM, P < 0.05, respectively). The thrombin (0. 03-1.0 U/ml)-evoked [Ca2+]i response was also enhanced in platelets from hypertensives in both the absence and presence of extracellular Ca2+. However, basal [Mg2+]i was higher in hypertensives than in normotensives (437 +/- 110 vs. 353 +/- 85 microM, P < 0.05), whereas serum Mg2+ was similar in the two groups. These results oppose the Mg2+ deficiency hypothesis in platelets in essential hypertension.

Cytosolic pH and calcium in Dahl salt-sensitive and salt-resistant rats: the relationship to plasma lipids

OBJECTIVE

To search for alterations of cytosolic pH and cell calcium handling in platelets and erythrocytes of Dahl rats susceptible and resistant to salt-induced hypertension.

DESIGN AND METHODS

Blood pressure, plasma lipids, platelet cytosolic calcium concentration ([Ca2+]i) and pH (pHi) together with thrombin-induced changes in these parameters as well as erythrocyte [Ca2+]i and 45Ca influx were determined in Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats aged 9, 15 and 24 weeks, which were fed a low-salt diet (0.3% NaCl), and in animals fed high-salt diet (4% NaCl) for 5-10 weeks since weaning.

RESULTS

With a low salt intake platelet pHi was lower in SS/Jr than it was in SR/Jr rats, whereas basal platelet [Ca2+]i was similar in rats of both strains. The difference in basal pHi between SS/Jr and SR/Jr rats increased progressively with age of animals. A high salt intake from youth did not influence platelet [Ca2+]i in rats of either strain but it caused an earlier decrease in pHi in SR/Jr than it did in SS/Jr rats. Thrombin stimulation induced similar elevations of pHi and [Ca2+]i in rats of both strains, irrespective of age, salt intake and response of blood pressure to salt intake. Erythrocyte 45Ca influx and [Ca2+]i were greater for SS/Jr rats but only the latter parameter was correlated positively to blood pressure. Both regulation of platelet pHi and erythrocyte Ca2+ handling were significantly related to plasma lipid levels.

CONCLUSIONS

Platelets of SS/Jr rats fed a low-salt diet were characterized by a lower basal cytosolic pHi but unchanged [Ca2+]i relative to those of SR/Jr rats. Hypertension induced by high salt intake was associated with increased erythrocyte [Ca2+]i but not with elevation of platelet [Ca2+]i or alteration of response to stimulation with thrombin.

Elevated lymphocyte cytosolic calcium in a subgroup of essential hypertensive subjects

Abnormalities of intracellular calcium homeostasis and sodium-proton exchange have been implicated in the pathophysiology of essential hypertension. To further define the nature of cytosolic calcium abnormalities and whether they relate to increased sodium-proton exchange in hypertension, we have studied peripheral lymphocytes from normotensive and hypertensive subjects. Lymphocyte cytosolic calcium was significantly increased (P < .01) in hypertensive compared with normotensive subjects while consuming a high salt diet. Using maximum likelihood analysis, we found that cytosolic calcium levels in our study population were not normally distributed and observed three modes (P < .02). The means of the first mode and the two upper modes were separated (+/-2 SD) at a cytosolic calcium level of 120 nmol/L. We conducted further analysis in the subgroups with cytosolic calcium levels > 120 nmol/L or < 120 nmol/L. The majority of the normotensive subjects (86%) and half of the hypertensive subjects (52%) had levels < 120 nmol/L. Clinical characteristics of the two subgroups did not differ. Subjects with levels < 120 nmol/L had a rise in cytosolic calcium when changed to a low salt diet; those with levels > 120 nmol/L did not show a change in cytosolic calcium but their blood pressure fell significantly with salt restriction. Hypertensive subjects also had increased sodium-proton exchange activity compared with normotensive subjects when both groups were studied in a high salt balance. A positive correlation between sodium-proton exchange and cytosolic calcium was observed in subjects with levels < 120 nmol/L. There was insufficient power to draw conclusions on this relationship in subjects with levels > 120 nmol/L. Thus, many hypertensive subjects have increased cytosolic calcium, but this abnormality is not associated with sodium-proton exchange activity in all individuals. The salt-induced change in cytosolic calcium in subjects with levels < 120 nmol/L and its link to sodium-proton exchange suggest regulation by factors involved in salt-volume homeostasis. Individuals with cytosolic calcium > 120 nmol/L, most of whom were hypertensive, may have abnormalities in this regulation, contributing to hypertension.

Platelet Ca2+ is not increased in stroke-prone spontaneously hypertensive rats: comparative study with spontaneously hypertensive rats

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.

Antihypertensive therapy and arterial function in experimental hypertension

1. Alterations in the function of the endothelium and arterial smooth muscle may be important in the establishment of hypertension. Thus, the possible favorable influences of blood pressure-lowering agents on vascular responsiveness may be important in the chronic antihypertensive actions of these compounds. 2. A number of reports have suggested that ACE inhibitors can improve arterial function in hypertension, whereas the knowledge about the vascular effects of other antihypertensive drugs, like beta-blockers, calcium channel blockers, and diuretics remains rather limited. 3. In this article, the effects of antihypertensive therapy on arterial function in human and experimental hypertension are reviewed.

Intracellular calcium and blood pressure: comparison between primary hyperparathyroidism and essential hypertension

Intracellular calcium has been reported to be increased in essential hypertension, and thought to play a role in its genesis through facilitation of vascular smooth muscle contraction. Since hypertension is more prevalent in primary hyperparathyroidism, intracellular calcium may also be increased in this condition. To investigate whether the hyperparathyroid condition, i.e., hypercalcemia and increased PTH per se, could be associated with high intracellular calcium, we measured intracellular calcium in platelets with the Quin-2 AM fluorometric method in 11 normotensive patients with primary hyperparathyroidism, 15 patients with essential hypertension, and 18 normal controls, all matched for age and sex. We repeated the measurements in 9 of the hyperparathyroid patients after successful surgery. We found that intracellular calcium was higher in normotensive patients with primary hyperparathyroidism than in normal controls (198 +/- 24 vs 113 +/- 11 nM, p < 0.05), but lower than in patients with essential hypertension (198 +/- 24 vs 286 +/- 38 nM, p < 0.05). Successful removal of a parathyroid adenoma decreased intracellular calcium from 215 +/- 22 to 116 +/- 19 nM, (p < 0.01). In the patients with primary hyperparathyroidism, intracellular calcium was strongly correlated with the levels of PTH (r = 0.87, p < 0.01), but not with the total serum calcium levels (r = 0.04, NS). The decrease in intracellular calcium after parathyroidectomy was also strongly correlated with the decrease in PTH (r = 0.84, P < 0.01), but not with the decrease in total serum calcium (r = 0.16, NS). In the patients with essential hypertension, intracellular calcium correlated well with systolic (r = 0.69, p < 0.01), diastolic (r = 0.76, p < 0.01) and especially mean arterial pressure (r = 0.86, P < 0.01). There was no correlation between blood pressure and intracellular calcium in the patients with primary hyperparathyroidism. We conclude that normotensive patients with primary hyperparathyroidism, as well as patients with essential hypertension, can have increased concentrations of intracellular calcium in platelets. The correction of the hyperparathyroid condition normalizes intracellular calcium concentration. The close correlation between PTH and intracellular calcium suggests that PTH may act as a ionophore for calcium entry into cells. Whether the increased levels of intracellular calcium may reflect a pre-hypertensive condition in normotensive patients with primary hyperparathyroidism remains to be determined.

Augmented Ca2+ mobilization is a hypertensive trait discriminated from a 'major gene' in backcross analysis between SHR and Donryu rats

1. Blood pressure and Ca2+ mobilization were significantly greater in SHR than in Donryu and F1 rats. 2. Backcross linkage analysis between spontaneously hypertensive rats and normotensive Donryu rats was performed to dissect polygenic hypertensive traits and to detect the existence of a single 'major gene'. 3. Cluster and discriminant analysis of a scattergram of blood pressure versus Ca2+ mobilization classified the backcrossed rats into two groups. The two groups were referred to the higher group and the lower group with regard to their relative blood pressure values. 4. Blood pressure was correlated with Ca2+ mobilization in each group; the correlation coefficients were 0.41 for the higher group (P < 0.01) and 0.71 for the lower group (P < 0.0001).

Effect of central amiloride infusion on mineralocorticoid hypertension

There is strong evidence from different types of studies, including the discrete infusion of agonists and antagonists and ablation of specific brain areas or transmitter-type neurons, that mineralocorticoids, in excess, act in the brain to elevate blood pressure. Aldosterone enhances the entry of Na+ through amiloride-sensitive Na+ channels in some mineralocorticoid-sensitive transport epithelial cells. To define possible cellular mechanisms involved in central mineralocorticoid action, benzamil, an amiloride analogue with selective affinity for the Na+ channel, was continuously infused intracerebroventricularly in three mineralocorticoid-dependent hypertension models in Sprague-Dawley rats, the continuous subcutaneous infusion of aldosterone, the intracerebroventricular infusion of aldosterone, and the ingestion of carbenoxolone, a synthetic licorice analogue. The intracerebroventricular infusion of 0.3 and 0.5 micrograms/h of benzamil, doses that did not have an adverse effect on growth and that had no effect on the blood pressure when infused subcutaneously, prevented the increase in blood pressure in these models. The infusion of these levels of benzamil had no effect on urine volume even in those animals in which it prevented an increase in blood pressure. These data suggest that the central effects of mineralocorticoids on blood pressure are mediated, at least in part, by the effects of mineralocorticoids on amiloride-sensitive sodium transport.

In vivo effect of calcitriol on calcium transport and calcium binding proteins in the spontaneously hypertensive rat

The abnormal intestinal Ca2+ transport reported in spontaneously hypertensive rats (SHR) has been attributed to decreased responsiveness to calcitriol. We reexamined this hypothesis by studying the calcitriol regulation of SHR duodenal calbindin-D9K and calmodulin and the relation of calcitriol to Ca2+ uptake by isolated enterocytes. SHR and normotensive Wistar-Kyoto (WKY) rats were injected with either 50 ng/d calcitriol (vit-D) or vehicle alone (control) for 3 days. Decreased calbindin-D9K (P < .001) and cellular Ca2+ flux (P < .001) were observed in control SHR. Calcitriol increased total cell and brush border calbindin-D9K (P < .0001); this variation paralleled plasma calcitriol levels in both strains. In contrast, Ca2+ flux, which increased in vit-D animals, remained lower in SHR for plasma calcitriol levels similar to those in WKY rats. Immunoreactive calmodulin was similar in both strains whether assayed in total cell or brush border membranes. In contrast, when measured by ligand blotting (45Ca), calmodulin was lower in SHR than in WKY rats (P < .01), suggesting the existence of a calmodulin pool with reduced Ca2+ binding capacity in the hypertensive strain. Calcitriol had no effect on calmodulin in either strain. In conclusion, Ca2+ binding protein regulation by calcitriol is normal in the SHR, and decreased hormone responsiveness cannot account for the defective duodenal calcium transport of this experimental model of hypertension.

Enhancement of arterial relaxation by long-term atenolol treatment in spontaneously hypertensive rats

1. The effects of long-term atenolol (25 mg kg-1 day-1) therapy on arterial function were studied in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The 14-week treatment attenuated the increase in blood pressure by approximately 30 mmHg in SHR, but did not affect blood pressure in WKY rats. 2. Responses of mesenteric arterial rings in vitro were examined at the end of the study. The relaxation to acetylcholine was similar in WKY rats and atenolol-treated SHR and more pronounced than in untreated SHR, whereas the relaxation to the nitric oxide donor 3-morpholinosydnonimine (SIN-1) was comparable in all study groups. Moreover, after maximal relaxations to acetylcholine, marked recontractions developed in untreated SHR but not in the other groups. Vasorelaxation to isoprenaline was also attenuated in SHR and was moderately improved by the atenolol therapy. 3. Arterial relaxation induced by return of potassium to the organ bath upon precontractions elicited by potassium-free solution were used to evaluate vascular smooth muscle Na+, K+-ATPase. The rate of potassium relaxation was fastest in WKY rats and was also faster in atenolol-treated than in untreated SHR. 4. The ability of vascular smooth muscle to sequester calcium was evaluated by eliciting responses to caffeine or noradrenaline after loading periods in different organ bath calcium concentrations. The subsequent contractions were lower in untreated SHR than in WKY rats, and augmented in SHR by the atenolol treatment. 5. Smooth muscle contractions to noradrenaline were comparable in SHR and WKY rats, while atenolol treatment slightly increased the maximal response to this agonist in SHR. Responses to potassium chloride were not affected by atenolol and contractions following cumulative re-addition of calcium to the organ bath after precontraction with potassium chloride and noradrenaline in calcium free solution were comparable in all study groups.6. In conclusion, the moderate antihypertensive effect of atenolol in SHR was accompanied by enhancement of beta-adrenoceptor-mediated and normalization of endothelium-dependent arterial relaxation.Furthermore, ability to sequester calcium into cellular stores, and function of Na+,K+-ATPase were augmented in vascular smooth muscle. Therefore, the present results suggest that the long-term blood pressure-lowering action of atenolol in this type of genetic hypertension is accompanied by improved arterial relaxation and normalization of endothelial function.

Effect of dietary magnesium supplementation on intralymphocytic free calcium and magnesium in stroke-prone spontaneously hypertensive rats

The effects of dietary magnesium (Mg) supplementation on intralymphocytic free Ca2+ ([Ca2+]i) and Mg2+ ([Mg2+]i) were examined in the stroke-prone spontaneously hypertensive rats (SHRSP) at the age of 10 weeks. After 40 day Mg supplementation (0.8% Mg in the diet), systolic blood pressure (SBP) was significantly lower in Mg supplemented group (Mg group) than the control group (0.2% Mg). [Ca2+]i was significantly lower and [Mg2+]i was significantly higher in Mg group than in the control group. Further, [Ca2+]i was positively and [Mg2+]i was negatively correlated with SBP. These results suggest that dietary Mg supplementation modifies [Ca2+]i and [Mg2+]i, and modulates the development of hypertension.

Dietary calcium and blood pressure in experimental models of hypertension. A review

More than 80 studies have reported lowered blood pressure after dietary calcium enrichment in experimental models of hypertension. The evidence presented here suggests that dietary calcium may act concurrently through a number of physiological mechanisms to influence blood pressure. The importance of any given mechanism may vary depending on the experimental model under consideration. Supplemental dietary calcium is associated with reduced membrane permeability, increased Ca(2+)-ATPase and Na,K-ATPase, and reduced intracellular calcium. These results suggest that supplemental calcium may limit calcium influx into the cell and improve the ability of the VSMC to extrude calcium. This could be a direct effect of calcium on the VSMC or an indirect effect mediated hormonally. The calcium-regulating hormones have all been found to have vasoactive properties and therefore may influence blood pressure. Furthermore, CGRP and the proposed parathyroid hypertensive factor are both vasoactive substances that are responsive to dietary calcium. Therefore, diet-induced variations in calcium-regulating hormones may influence blood pressure. Modulation of the sympathetic nervous system is another important way that dietary calcium can influence blood pressure. There is evidence of altered norepinephrine levels in the hypothalamus as a consequence of manipulations of dietary calcium as well as changes in central sympathetic nervous system outflow. Dietary calcium has also been shown to specifically modify alpha 1-adrenergic receptor activity in the periphery. In some experimental models of hypertension, dietary calcium may alter blood pressure by changing the metabolism of other electrolytes. For example, the ability of calcium to prevent sodium chloride-induced elevations in blood pressure may be attributed to natriuresis. However, natriuresis does not account for all of the interactive effects of calcium and sodium chloride on blood pressure. Sodium chloride-induced hypertension may be due in part to calcium wasting and subsequent elevation of calcium-regulating hormones. Chloride is an important mediator of this effect because it appears that sodium does not cause calcium wasting when it is not combined with chloride. More attention to the central nervous system effects of dietary calcium is needed. Not only can calcium itself influence neural function, but many of the calcium-regulating hormones appear to affect the central nervous system. The influence of calcium and calcium-regulating hormones on central nervous system activity may have important implications for blood pressure regulation and also may extend to other aspects of physiology and behavior.

Arterial smooth muscle responses in adult and moderately aged spontaneously hypertensive rats

In order to further clarify differences between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats as well as the effects of ageing, vascular smooth muscle responses of mesenteric arterial rings and intracellular free calcium concentration ([Ca2+]i) in platelets and lymphocytes were studied in 20-week-old and 32-week-old animals. Arterial contractile responses induced by noradrenaline and potassium chloride were comparable in 20-week-old SHR and WKY rats, whereas at 32 weeks of age maximal contractile force generation to both of these agents was clearly lower in SHR. In both age groups the calcium entry blocker nifedipine was more effective in inhibiting potassium chloride-evoked responses in SHR than in WKY rats, and arterial relaxation responses by endothelium-dependent (acetylcholine) and endothelium-independent (nitroprusside, isoprenaline) mechanisms were more pronounced in WKY rats when compared with SHR. The ability of vascular smooth muscle cells to sequester calcium was evaluated by first depleting cellular calcium stores with maximal contractions to noradrenaline in calcium-free buffer, whereafter calcium was returned to the organ bath. After a 10 min. calcium loading period the arterial rings were rechallenged with noradrenaline. Both in 20-week-old and 32-week-old rats these responses were less marked in SHR than in WKY rats, suggesting reduced ability of smooth muscle cells to sequester calcium. In addition, platelets and lymphocytes were used as cell models to examine [Ca2+]i in the experimental groups by the fluorescent indicator quin-2. In these two cell types [Ca2+]i was higher in SHR than in WKY rats in both of the age groups studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Na(+)-Ca2+ exchanger in arteries: identification by immunoblotting and immunofluorescence microscopy

Antibodies raised against dog cardiac Na(+)-Ca2+ exchanger were employed to determine the presence and distribution of the exchanger in arterial smooth muscle (ASM) cells. The antiserum cross-reacted with protein bands of approximately 70, 120, and 150-160 kDa from the membranes of ASM cells, as well as heart sarcolemma. A cardiac Na(+)-Ca2+ exchanger cDNA probe hybridized to 7-kilobase (kb) mRNA from myocytes of the mesenteric artery. Thus ASM cells possess a "cardiac type" Na(+)-Ca2+ exchanger. The relative amounts of 7-kb mRNA and antigen detected on Northern and Western blots, respectively, however, indicate that vascular myocytes contain much less of this transporter than do cardiac myocytes. Immunofluorescence studies on cultured arterial myocytes suggest that the exchanger molecules are organized in reticular patterns over the cell surfaces. A similar pattern is observed when cells are stained for sarcoplasmic reticulum (SR) Ca(2+)-ATPase. This raises the possibility that the exchanger in the plasmalemma of arterial myocytes may be associated, perhaps functionally as well as structurally, with the underlying SR. The antiserum also cross-reacted with endothelial cell membranes, but labeling was lighter and more diffuse than in the myocytes.

Intralymphocytic free calcium and magnesium in stroke-prone spontaneously hypertensive rats and effects of blood pressure and various antihypertensive agents

1. Free Ca2+ ([Ca2+]i) and Mg2+ ([Mg2+]i) were measured in peripheral lymphocytes from stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY) at the age of 5, 7 and 17 weeks, from various antihypertensive agents-treated SHRSP, and from secondary hypertensive WKY. 2. At the age of 5 weeks, no difference was observed in systolic blood pressure (SBP), or lymphocyte [Ca2+]i and [Mg2+]i between SHRSP and WKY. At the age of 7 or 17 weeks, SBP and [Ca2+]i of SHRSP were significantly higher than in WKY, and at the age of 17 weeks, [Mg2+]i of SHRSP was significantly lower than in WKY. Further, [Ca2+]i or [Mg2+]i was positively or negatively correlated to SBP, and [Mg2+]i was negatively correlated to [Ca2+]i. 3. SBP of SHRSP fell significantly after antihypertensive treatment with calcium antagonist, angiotensin-converting enzyme (ACE) inhibitor or hydralazine for 40 days. [Ca2+]i was significantly lower in calcium antagonist and hydralazine groups, and tended to be low in ACE inhibitor group. These four groups showed no difference in [Mg2+]i. 4. After 40-day administration of NG-nitro-L-arginine (L-NNA), WKY developed severe hypertension, but there were no significant differences in lymphocyte [Ca2+]i and [Mg2+]i between the L-NNA treated and non-treated groups. 5. These results suggested that increased lymphocyte [Ca2+]i and decreased [Mg2+]i observed in SHRSP are not only secondary to hypertension but possibly related to a basic genetic abnormality of divalent cation handling.

Quinapril treatment and arterial smooth muscle responses in spontaneously hypertensive rats

1 The effects of long-term angiotensin-converting enzyme inhibition with quinapril on arterial function were studied in spontaneously hypertensive rats, Wistar-Kyoto rats serving as normotensive controls. 2 Adult hypertensive animals were treated with quinapril (10 mg kg-1 day-1) for 15 weeks, which reduced their blood pressure and the concentrations of atrial natriuretic peptide in plasma and ventricular tissue to a level comparable with that in normotensive rats. 3 Responses of mesenteric arterial rings in vitro were examined at the end of the study. Compared with normotensive and untreated hypertensive rats, responses to noradrenaline were attenuated in hypertensive animals on quinapril, both force of contraction and sensitivity being reduced. Quinapril also attenuated maximal contractions but not sensitivity to potassium chloride. Nifedipine less effectively inhibited vascular contractions in normotensive and quinapril-treated than in untreated hypertensive rats. 4 Arterial relaxation responses by endothelium-dependent (acetylcholine) and endothelium-independent (sodium nitrite, isoprenaline) mechanisms were similar in normotensive and quinapril-treated rats and more pronounced than in untreated hypertensive rats. 5 Cell membrane permeability to ions was evaluated by means of potassium-free solution-induced contractions of endothelium-denuded denervated arterial rings. These responses were comparable in normotensive and quinapril-treated rats and less marked than in untreated hypertensive rats. 6 Intracellular free calcium concentrations in platelets and lymphocytes, measured by the fluorescent indicator quin-2, were similar in normotensive and quinapril-treated rats and lower than in untreated hypertensive rats. 7 In conclusion, quinapril treatment improved relaxation responses and attenuated contractions in arterial smooth muscle of hypertensive rats. These changes may be explained by diminished cytosolic free calcium concentration, reduced cell membrane permeability, and alterations in dihydropyridine-sensitive calcium channels following long-term angiotensin-converting enzyme inhibition.

Normal thrombin binding leads to greater fibrinogen binding and increased platelet aggregation in spontaneously hypertensive rats

This study was conducted to determine the mechanisms of increased platelet reactivity to thrombin in hypertension. Thrombin induced significantly greater platelet aggregation in spontaneously hypertensive (SHR) than in normotensive (Wistar Kyoto, WKY) rats. Fibrinogen and thrombin binding to platelets was determined using [125I]-fibrinogen and [125I]-thrombin respectively. Increased platelet aggregation in SHR correlated with thrombin-induced greater binding of fibrinogen to SHR than to WKY platelets. However, the number of thrombin receptors (binding sites/platelet) in WKY (19,500 +/- 3,000) and SHR (23,100 +/- 3,000) as well as thrombin dissociation constants were statistically similar in WKY (1.17 +/- 0.2 microM) and SHR (1.62 +/- 0.27 microM) platelets. Fura 2/AM, a fluorescent calcium indicator, loaded platelets were used to quantify the platelet ionized calcium ([Ca2+]i). The [Ca2+]i in unstimulated SHR and WKY platelets was essentially the same. In a calcium poor medium, thrombin-induced a 35% greater increase in [Ca2+]i in SHR than in WKY platelets. These data, taken together with our earlier observations that thrombin induces a significantly greater hydrolysis of phosphoinositide (Thromb. Res. 49, 5-21, 1988), lead us to suggest that thrombin-induced increased generation of inositol 1,4,5-trisphosphate and diacylglycerol induces greater fibrinogen binding and consequently increased aggregation in SHR than WKY platelets. The finding that the thrombin binding isotherms are similar in WKY and SHR platelets suggests that increased platelet sensitivity to thrombin in hypertension may be due to altered signal transduction and not due to changes in the number or affinity of thrombin receptors.