In the guinea-pig vas deferens, isoprenaline (ISO) can exert significantly enhanced effects on voltage-dependent Ca2+ channel current carried by Ba2+ (IBa) via beta-adrenoceptor activation. Voltage-dependent Ba2+ (IBa) and K+ currents (I K) were recorded in the preparation voltage-clamped in a Krebs solution replaced Ca2+ by Ba2+ (Ba2+ solution) of 36 degrees C. At a holding potential of -40 mV, ISO markedly increased IBa evoked by depolarizing pulses, whereas it also increased I K at a holding potential of -20 mV so as to inactivate Ca2+ channel. This ISO-induced enhancement of IBa seems to be contradictory to the suppression of contraction by beta-adrenoceptor activation in normal Krebs solution.
Adrenergic beta-Agonists Animals