The vicissitudes of the pacemaker current IKdd of cardiac Purkinje fibers

摘要

The pacemaker potential in cardiac Purkinje fibers has been attributed to the decay of the potassium current IKdd . An alternative proposal is that the hyperpolarization-activated current If underlies the pacemaker potential in all cardiac pacemakers . The aim of this review is to retrace the experimental development related to the pacemaker mechanism in Purkinje fibers with reference to findings about the pacemaker mechanism in the sinoatrial node. Major experimental data were attributed to K + depletion in narrow extracellular spaces which would result in a time-dependent decay of the inward rectifier current IK1. In order to avoid such a postulated depletion, Ba~(2+) was used to block the decay of IK1. However, Ba2 + had also blocked IKdd (and not only IK1). In single Purkinje cells in the absence of Ba2 +, IKdd was present in the pacemaker potential range and reversed at EK. In the presence of Ba2 +, IKdd was blocked and If appeared at potentials negative to the pacemaker range . The pacemaker potential behaves in a manner consistent with the underlying IKdd but not with If. It is concluded that the large boy of evidence supports the pacemaker role of IKdd (but not of If) in Purkinje fibers