MEMBRANE CURRENTS ELICITED BY THE ORGANIC CALCIUM-CHANNEL BLOCKER VERAPAMIL IN NATIVE AND RAT-BRAIN RNA-INJECTED OOCYTES OF XENOPUS-LAEVIS

For further analysis of the action of the diphenylalkylamine derivate verapamil (GAS 152-11-4), the ability of. verapamil to elicit membrane currents by itself was investigated in native and rat brain RNA-injec ted oocytes of Xenopus laevis. Administration of verapamil elicited in ward currents which remained constant or increased slightly during ong oing application. In native and RNA-injected oocytes the current respo nses were similar in shape, but larger in size in RNA-injected oocytes . The currents increased up to the maximal tested concentration of 1 m mol/l verapamil; the threshold concentration was below 80 mu mol/l. Af ter removal of follicular tissues the verapamil response was nearly do ubled. During verapamil administration the input resistance was increa sed up to 1.7 of the initial value. The current response to verapamil can be subdivided into an early and late component. The equilibrium po tential of the early component ranged between -80 and -110 mV; the lat e component which increased slightly during verapamil application, had an equilibrium potential between 0 and -20 mV. Under the influence of potassium channel blockers (terraethylammonium and cesium chloride) o r chloride channel blockers (anthracene-9-carbonic acid and the indany loxy-acetic acid derivative IAA-94) the verapamil induced currents wer e reduced. Thus, the results indicate that beside the calcium channel- blocking effect, verapamil can induce currents by itself, presumably b y acting on the potassium and chloride leakage.