Interaction of phenoxybenzamine with muscarinic receptors and calcium channels

Phenoxybenzamine (POB, 10(-6) - 10(-4) M) inhibited the responses of guinea pig ileal longitudinal smooth muscle to both muscarinic agonists and K+-depolarization but was more effective against the agonist-induced responses. POB inhibited binding of both the muscarinic antagonist [3H]quinuclidinyl benzilate (QNB) and the Ca2+ channel antagonist [3H]nitrendipine and was, paralleling its effects on mechanical responses, more effective against [3H]QNB binding. POB reduced specific [3H]QNB binding by a reduction in Bmax with no change in KD, but inhibited [3H]nitrendipine binding by reducing KD with no effect on Bmax. It is suggested that the activity of POB against Ca2+ channels may underlie the ability of POB, and other 2-halogenoethylamines, to inhibit a wide variety of apparently discrete pharmacological events.