Calmodulin abolishes the changes in Ca2+ binding and transport by heart sarcolemmal membranes of spontaneously hypertensive rats

Both Ca2+ transport and binding properties of heart sarcolemmal membranes are altered in spontaneously hypertensive rats (SHR) when compared to their normotensive controls (WKY). The effects of calmodulin on these two processes were studied at free calcium concentrations presumed to be the physiological levels in the cytosol. At a calcium concentration of 2.10(-8)M, calmodulin did not significantly modify either binding or ATP-dependent accumulation of calcium by membranes of both origins. In contrast, at a free calcium concentration of 4.10(-7)M, calmodulin enhanced the calcium binding to SHR membranes and the ATP-dependent calcium transport by SHR and WKY membranes. Differences in calcium binding and ATP-dependent accumulation between the two substrains were suppressed in presence of calmodulin. These data demonstrate that modifications in calcium handling by SHR cardiac plasma membranes might be due to altered intracellular content or function of calmodulin in SHR.