Responses of cytosolic free calcium to ADP in platelets of spontaneously hypertensive rats.
 Abnormalities of Ca2+ handling have been reported in patients with essential hypertension and in spontaneously hypertensive rats (SHR).
 In this study, responses of cytosolic Ca2+ to ADP in platelets of SHR were examined.
 Four- and seven-week-old male SHR and age- and sex-matched Wistar-Kyoto rats (WKY) were used.
 Basal levels of the intracellular Ca2+ concentration in platelets and responses to ADP were estimated using fluorescent indicator fura-2 in the medium containing 1 mmol/L CaCl2 and Ca2(+)-free buffer with 1 mmol/L EGTA.
 Basal levels of platelet cytosolic Ca2+ of SHR were significantly higher than those of WKY at 4 and 7 weeks of age in the presence of external Ca2+.
 However, no significant difference was observed in basal levels of platelet cytosolic Ca2+ in the Ca2(+)-free EGTA-containing buffer between SHR and WKY.
 The peak cytosolic Ca2+ concentration evoked by ADP was significantly diminished in SHR compared with WKY in the absence of external Ca2+, whereas the responses of platelet cytosolic Ca2+ to ADP were similar in SHR and WKY in the presence of external Ca2+.
 These results suggest that release from intracellular Ca2+ store is reduced in SHR and that the regulation of cytosolic Ca2+ in SHR is more dependent on extracellular Ca2+ compared with WKY.
