Calcium-channel antagonist binding to isolated vascular smooth muscle membranes

The binding characteristics of the calcium-channel antagonist nitrendipine, an analog of nifedipine, have been measured in plasma membrane enriched microsomal fractions from the canine thoracic aorta, canine mesenteric artery, and rat mesenteric artery. The dissociation constants, KD, for the high-affinity binding sites were, respectively, 0.308, 0.254, and 0.101 nM and Bmax values for binding capacity were 20.3, 25.0, and 18.0 fmol/mg of microsomal protein. Studies with isolated tissues, in which the sensitivity of the high potassium mechanical response to nitrendipine was determined, indicate that the apparent KD for nitrendipine in the canine mesenteric artery, as reflected by the IC50 (mean inhibition constant) value, is 4.5 – 5.3 nM and for the rat mesenteric artery 2.5 – 6.6 nM.