The action of beta-adrenoceptor antagonist penbutolol on the pacemaker current of cardiac Purkinje fibres.
The action of beta-adrenoceptor antagonist penbutolol on the current underlying pacemaker activity in cardiac Purkinje fibres was analysed using the voltage clamp technique described by DECK et al. (1964). After the application of adrenalin, beta-blockers are able to counteract the well known shift of the s-kinetics of the pacemaker current. However, without any prior application of adrenalin the beta-blocker Penbutolol has no effect on these kinetics except for a small depression of the amplitude of the pacemaker current tails. The rectifier properties of the pacemaker current and the negative slope of the fully activated current voltage relationship of iK2 are unchanged. Penbutolol is able--even after a longer period of washout (about 60-90 min was necessary)--to protect the beta-adrenoceptors from the action of adrenalin (HASHIMOTO et al., 1979). These findings suggest that beta-blockers are competitive inhibitors of beta-stimulators and further support the notion that the pacemaker current in cardiac Purkinje fibres is controlled by beta-adrenoceptors.
D000818:Animals; D004837:Epinephrine / Q000494:pharmacology; D006329:Heart Conduction System / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D010394:Penbutolol / Q000494:pharmacology*; D011412:Propanolamines / Q000494:pharmacology*; D011690:Purkinje Fibers / Q000187:drug effects / Q000502:physiology*; D012756:Sheep
D011412:Propanolamines; D010394:Penbutolol; D004837:Epinephrine