Decreased dihydropyridine receptor number in hypertensive rat vascular muscle cells

To further investigate the altered function of Ca²⁺ channels in vascular muscle cells in hypertension, a novel fluorescently labeled dihydropyridine was used with ultrahigh-sensitivity photometry to study dihydropyridine binding sites on the surface membrane of living vascular muscle cells from stroke-prone spontaneously hypertensive rats and their normotensive controls. Fluorescent nitrobenzoxadiazol-6-dihydropyridine in concentrations of 1 to 100 nmol/L bound specifically to vascular muscle cells' Ca²⁺ channels, and was displaced by the unlabeled dihydropyridine analogue or nisoldipine (10 μmol/L). Stroke-prone spontaneously hypertensive rat vascular muscle cells showed significantly decreased binding of nitrobenzoxadiazol-6- dihydropyridine compared with normotensive National Institutes of Health rats. Decreased binding of dihydropyridine by vascular muscle cells from stroke-prone spontaneously hypertensive rats (cells that in other studies show increased Ca²⁺ channel function) indicates a change in channel regulation that is possibly due to a deficiency in the inactivation mechanism, consistent with our earlier electrophysiological studies reporting deficiencies in Ca²⁺-dependent inactivation in genetic hypertension. These data demonstrate decreased numbers of localized sites of dihydropyridine binding of the sarcolemma of living vascular muscle cells, and support the hypothesis that Ca²⁺ channel alterations may significantly contribute to the molecular etiology of genetic hypertension.