- 作者: Youyin Choy; Eugene M. Kim ; 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 aim of the present experiments was to study the characteristics and mechanisms of the rhythm induced by overdrive ('overdrive excitation', ODE) in the sinoatrial node (SAN) superfused in high [K+]o (8-14 mM). It was found that: (1) overdrive may induce excitation in quiescent SAN and during a slow drive; (2) in spontaneously active SAN, overdrive may accelerate the spontaneous discharge; (3) immediately after the end of overdrive, a pause generally precedes the onset of the induced rhythm; (4) during the pause, an oscillatory potential (Vos) may be superimposed on the early diastolic depolarization (DD); (5) during the subsequent late DD, a different kind of oscillatory potential appears near the threshold for the upstroke (ThVOS) which is responsible for the initiation of spontaneous activity; (6) once started, the induced rhythm is fastest soon after overdrive; (7) faster drives induce longer and faster spontaneous rhythms; (8) the induced action potentials are slow responses followed by DD with a superimposed Vos, but ThVOS is responsible for ODE; (9) the induced rhythm subsides when ThVOS miss the threshold and gradually decay; (10) low [Ca2+]o abolishes ODE; (11) in quiescent SAN, high [Ca2+]o induces spontaneous discharge through ThV0S and increases its rate by enhancing Vos and shifting the threshold to more negative values, and (12) tetrodotoxin abolishes ODE as well as the spontaneous discharge induced by high [Ca2+]o. In conclusion, in K+-depolarized SAN, ODE may be present in the apparent absence of calcium overload, is Ca2+- and Na+-dependent and is mediated by ThVOS and not by Vos.
- 中文關鍵字: --
- 英文關鍵字: Sinoatrial node ; High potassium ; Overdrive excitation ; Oscillatory afterpotential and prepotential ; Calcium ; Tetrodotoxin ; Sodium