Polyamines allosterically modulate [3H]nitrendipine binding to the voltage-sensitive calcium channel in rat brain

The effects of polyamines on radioligand binding to the slow voltage-dependent Ca2+ channel were studied using membranes from the rat cerebral cortex. [3H]Diltiazem binding was inhibited by arcaine (IC50 = 55 microM) and, in decreasing order of potency, by agmatine, spermidine, spermine and putrescine. Under control conditions, only spermidine and spermine allosterically inhibited [3H]nitrendipine binding while arcaine, agmatine and putrescine were inactive. Nevertheless, putrescine antagonized the effect of spermine as well as the allosteric effects of diltiazem and verapamil on the binding of [3H]nitrendipine, in a manner analogous to that shown previously for Ca2+. Thus, polyamines may function as endogenous modulators of the voltage-dependent Ca2+ channel.