Characteristics of Specific Bindings of Nitrendipine and PN200–110 to Various Crude Membranes: Induction of Irreversible Bindings by UV Irradiation

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Abstract
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<(+)PN< (−)PN>Bay K 8644 (Bay) > verapamil (Ver) > diltiazem (Dil). In crude skeletal membranes only, PN caused significant stereo specific inhibition. The order of inhibitions of specific [3H] (+ )PN bindings to these crude membranes was generally (+ )PN > Nit ≫ (− )PN > Bay > Ver> Dil. In all these crude membranes, UV irradiation completely prevented decrease in the amount of specific binding of [3H]Nit on addition of a large excess of unlabeled Nit and reduced the decrease of specific [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.