- 作者: Jeffrey P. Sternlicht; Mario Vassalle
- 作者服務機構: Department of Physiology, State University of New York, Health Science Center, Brooklyn, N.Y., USA
- 中文摘要: --
- 英文摘要: The mechanisms of the hyperpolarizing and depolarizing actions of cesium were studied in cardiac Purkinje fibers perfused in vitro by means of a microelectrode technique under conditions that modify either the Na+-K+ pump activity or If. Cs+ (2 mM) inconsistently increased and then decreased the maximum diastolic potential (MDP); and markedly decreased diastolic depolarization (DD). Increase and decrease in MDP persisted in fibers driven at fast rate (no diastolic interval and no activation of If). In quiescent fibers, Cs+ caused a transient hyperpolarization during which elicited action potentials were followed by a markedly decreased undershoot and a much reduced DD. In fibers depolarized at the plateau in zero [K+]o (no If), Cs+ induced a persistent hyperpolarization. In 2 mM [K+]o, Cs+ reduced the undershoot and suppressed spontaneous activity by hyperpolarizing and thus preventing the attainment of the threshold. In 7 mM [K+]o, DD and undershoot were smaller and Cs+ reduced them. In 7 and 10 mM [K+]o, Cs+ caused a small inconsistent hyperpolarization and a net depolarization in quiescent fibers; and decreased MDP in driven fibers. In the presence of strophanthidin, Cs+ hyperpolarized less. Increasing [Cs+]0 to 4, 8 and 16 mM gradually hyperpolarized less, depolarized more and abolished the undershoot. We conclude that in Purkinje fibers Cs+ hyperpolarizes the membrane by stimulating the activity of the elec-trogenic Na+-K+ pump (and not by suppressing If); and blocks the pacemaker potential by blocking the undershoot, consistent with a Cs+ block of a potassium pacemaker current.
- 中文關鍵字: --
- 英文關鍵字: Purkinje fibers; Cesium; Na+-K+ pump; Pacemaker potential; High and low [K+]o; Strophanthidin; Sheep