Comparison of [3H]nitrendipine binding to heart membranes of normotensive and spontaneously hypertensive rats.

We compared the binding properties of [3H]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, [3H]nitrendipine binds to a single class of binding sites with high affinity (Kd, approximately equal to 0.20 nM) and high capacity (Bmax, approximately equal to 96 fmol X mg protein-1). By contrast, in membranes of 24-week-old, SHR, Kd and Bmax increased significantly to 0.30 nM and 137 fmol X mg protein-1, respectively. Addition of 1 mM Ca2+ had no effect on [3H]nitrendipine binding in WKY but decreased the Kd value to 0.18 nM in 24-week-old SHR. Bmax remained 40% above the value in WKY. Inhibition and activation of specific binding by nifedipine and dilitiazem are identical in both strains. We conclude that the differences in [3H]nitrendipine binding in hearts of aged SHR are due to a decreased Ca2+ content and might reflect a functional adaptation.