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 verapamil (CAS 152-11-4), the ability of verapamil to elicit membrane currents by itself was investigated in native and rat brain. RNA-injected oocytes of Xenopus laevis. Administration of verapamil elicited inward currents which remained constant or increased slightly during ongoing application. In native and RNA-injected oocytes the current responses were similar in shape, but larger in size in RNA-injected oocytes. The currents increased up to the maximal tested concentration of 1 mmol/l verapamil; the threshold concentration was below 80 mumol/l. After removal of follicular tissues the verapamil response was nearly doubled. During verapamil administration the input resistance was increased up to 1.7 of the initial value. The current response to verapamil can be subdivided into an early and late component. The equilibrium potential of the early component ranged between -80 and -110 mV; the late component which increased slightly during verapamil application, had an equilibrium potential between 0 and -20 mV. Under the influence of potassium channel blockers (tetraethylammonium and cesium chloride) or chloride channel blockers (anthracene-9-carbonic acid and the indanyloxy-acetic acid derivative IAA-94) the verapamil induced currents were reduced. Thus, the results indicate that beside the calcium channel-blocking effect, verapamil can induce currents by itself, presumably by acting on the potassium and chloride leakage.