AJP - Heart and Circulatory Physiology, Vol 251, Issue 5 1056-H1061, Copyright © 1986 by American Physiological Society
Depolarizing effects of catecholamines in quiescent sheep cardiac Purkinje fibers
S. Terris, J. A. Wasserstrom and H. A. Fozzard
Isoproterenol reversibly depolarizes quiescent sheep cardiac Purkinje
fibers, in contrast to its reported hyperpolarizing effect in many
excitable tissues. The depolarization is inhibited by drugs that block beta
1-adrenergic receptors. Tetrodotoxin and verapamil have no effect on the
isoproterenol-induced depolarization. Cesium reduced the
isoproterenol-induced depolarization by 74%. The voltage dependency of
activation of a current component called If, measured under voltage clamp,
was shifted in the depolarizing direction by isoproterenol. No evidence was
found to support the suggestion made for other tissues that the Na+-K+ pump
is stimulated by isoproterenol. These data suggest that in quiescent sheep
Purkinje fibers the isoproterenol-induced depolarization reflects
activation of a pacemaker current.
