Comparison of [3H]Nitrendipine Binding to Heart Membranes of Normotensive and Spontaneously Hypertensive Rats

We compared the binding properties of [H]nitrendipine in heart membranes from 9− and 24-week-old spontaneously hypertensive rats (SHR) and their normotensive controls (WKY). In native membranes of 9-week-old SHR and WKY and of 24-week-old WKY, [H]nitrendipine binds to a single class of binding sites with high affinity (Kd, ≊=0.20 n M) and high capacity (Bmax ≊96 fmol · mg protein). By contrast, in membranes of 24-week-old, SHR, Kd and Bmax increased significantly to 0.30 n M and 137 fmol · mg protein, respectively. Addition of 1 m M Ca had no effect on [H]nitrendipine binding in WKY but decreased the Kd value to 0.18 n M in 24-week-old SHR. Bmax remained 40% above the value in WKY. Inhibition and activation of specific binding by nifedipine and diltiazem are identical in both strains. We conclude that the differences in [H]nitrendipine binding in hearts of aged SHR are due to a decreased Ca content and might reflect a functional adaptation.