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 CaCl2and 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 intra-cellular Ca2+store is reduced in SHR and that the regulation of cytosolic Ca2+in SHR is more dependent on extracellular Ca2+compared with WKY. © 1990 by the American Journal of Hypertension, Ltd.