Electrophysiological and pharmacological evidence that peripheral type benzodiazepine receptors are coupled to calcium channels in the heart

PK 11195, an antagonist of the peripheral type benzodiazepine receptor, does not affect either the duration of the action potential or the tension of the guinea pig papillary muscle. However, it antagonized the effects of the calcium channel blockers, nitrendipine, verapamil, diltiazem, and of BAY K8644, a calcium channel agonist in this heart preparation. On the other hand, PK 11195 does not change the increase in the action potential duration provoked by the potassium channel blocker tetraethylammonium. RO5-4864, an agonist of the peripheral type benzodiazepine receptor, decreased the tension of the guinea pig papillary muscle. The effect was reversed by increasing extracellular Ca 2+ concentrations up to 4 mM. These results suggest that in the heart the peripheral type benzodiazepine receptors are coupled to calcium channels.