DIETARY SALT DECREASES CYTOSOLIC CALCIUM IN PLATELETS FROM DAHL SALT-SENSITIVE RATS

To determine whether abnormal cellular Ca2+ handling is involved in sa lt-induced hypertension of Dahl salt-sensitive rats (DS), we investiga ted Ca2+ handling in fura a-loaded platelets of DS and Dahl salt-resis tant rats (DR) fed a high-NaCl (8%) or a low-NaCl (0.3%) diet for 4 wk from 5 wk. of age. At 5 wk of age, blood pressure, resting cytosolic Ca2+ concentration ([Ca2+](i)), the thrombin-evoked increase in [Ca2+] (i) and the size of internal Ca2+ stores of DS were comparable with th ose of DR. After 4 wk on the diets, resting [Ca2+](i) of DS on high-Na Cl diet was lower than that of DS on low-NaCl diet, and there was no e ffect of high salt intake on resting [Ca2+](i) in DR. In DS, high salt intake attenuated the [Ca2+](i) response to thrombin in the presence of external Ca2+. In contrast, the [Ca2+](i) response to thrombin in t he absence of external Ca2+ was enhanced by high salt intake in DS. Th e size of internal Ca2+ stores was increased by high salt intake in DS but not in DR. These data suggest that it is not obligatory for hyper tension to be accompanied by an increase in platelet [Ca2+](i).