ROLE OF PLATELET CYTOSOLIC CALCIUM IN REGULATION OF BLOOD-PRESSURE IN PATIENTS ON CHRONIC-HEMODIALYSIS

We measured blood pressure, platelet cytosolic calcium concentration ([Ca2+]i) and vasoactive hormones in 20 anuric normotensive patients on chronic hemodialysis (HD) to clarify the role of cytosolic calcium in regulation of blood pressure. All measurements were performed at the end of HD (post-HD) and at the beginning of the next HD (pre-HD). During the HD-HD interval, mean blood pressure increased from 85 +/- 4 to 94 +/- 4 mm Hg (mean +/- SEM, p < 0.05), but the median [Ca2+]i in platelets did not show any significant change (133 +/- 5 vs. 136 +/- 5 nmol/l). Although all patients were within their ideal body weight at post-HD, platelet [Ca2+]i did not correlate with mean blood pressure. By contrast, platelet [Ca2+]i correlated with mean blood pressure (r = 0.489, p < 0.05) at pre-HD. Moreover, platelet [Ca2+]i at post-HD also correlated with changes in mean blood pressure during the HD-HD interval (r = 0.532, p < 0.05). In addition, there were negative correlations between platelet [Ca2+]i and plasma renin activity both post- and pre-HD (r = -0.652, p < 0.005; r = -0.673, p < 0.005; respectively). These results suggest that cytosolic calcium plays important roles in regulation of renin secretion and in the elevation of blood pressure induced by volume expansion in patients on chronic HD.