Characteristics of specific bindings of nitrendipine and PN200-110 to various crude membranes: induction of irreversible bindings by UV irradiation

The characteristics of the specific bindings of 3H]nitrendipine (Nit) and 3H](+)PN200-110 (PN) to crude membranes from rat skeletal, cardiac, and uterine muscle and whole brain were investigated, with special interest in the effect of UV irradiation on these bindings. The specific bindings of 3H]Nit and 3H](+)PN to these crude membranes were saturable and reversible. The specific bindings of 3H]Nit to all these membranes except crude skeletal membranes was maximum in the presence of 0.15 M NaCl plus 1 mM CaCl2 and minimal in the absence of these ions, but the specific bindings of 3H](+)PN to these crude membranes was not affected significantly by these ions. A calcium agonist and antagonists inhibited the specific bindings of 3H]Nit and 3H](+)PN to these crude membranes, the order of their inhibitory effects on specific 3H]Nit bindings being roughly Nit greater than or equal to (+)PN greater than or equal to (-)PN much greater than Bay K 8644 (Bay) greater than verapamil (Ver) greater than diltiazem (Dil). In crude skeletal membranes only, PN caused significant stereospecific inhibition. The order of inhibitions of specific 3H](+)PN bindings to these crude membranes was generally (+)PN greater than Nit greater than or equal to (-)PN greater than Bay much greater than Ver greater than or equal to Dil. In all these crude membranes, UV irradiation completely prevented decrease in the amount of specific binding of 3H](+)PN binding on addition of excess unlabeled (+)PN. These findings suggested that 3H]Nit and 3H](+)PN bind to voltage-sensitive calcium channels in crude membranes from rat skeletal, cardiac, and uterine muscle and whole brain, and that UV irradiation changes the specific bindings of 3H]Nit and 3H](+)PN from reversible to irreversible bindings.