- 作者: M. Vassalle; F. Valenzuela
- 作者服務機構: a Department of Physiology, State University; of New York Health Science Center, Brooklyn, N.Y., USA, and; b Departamento de Fisiologia, Instituto Nacional de Cardiologia, Mexico DF, Mexico
- 中文摘要: --
- 英文摘要: The role of the inward K+ rectifier in the repetitive activity at depolarized levels was studied in guinea pig single ventricular myocytes by voltage- and current-clamp methods. In action potentials arrested at the plateau by a depo- larizing current, small superimposed hyperpolarizing currents caused much larger voltage displacements than at the resting potential and sometimes induced a regenerative repolarization. Around一20 mV, sub- and supra- threshold repetitive inward currents were found. In the same voltage range, small hyperpolarizing currents reversed their polarity. During depolarizing voltage-clamp ramps, around-20 mV there was a sudden decrease in the out- ward current (Ins: current underlying the negative slope in the inward K+ recti- fier steady state I-V relation). During repolarizing ramps, the reincrease in outward current was smaller and slower. During depolarizing and repolarizing current ramps, sudden voltage displacements showed a similar asymmetry. Repetitive Ins could continue as long as the potential was kept at the level at which they appeared. Depolarizing voltage-clamp steps also caused repetitive Ins and depolarizing current steps induced repetitive slow responses. Cad- mium and verapamil reduced Ins amplitude during the depolarizing ramp. BRL 34915 (cromakalim), an opener of the ATP-sensitive K+ channel, elimi- nated the negative slope and Ins, whereas barium increased Ins frequency (an effect abolished by adding BRL). Depolarization-induced slow responses per- sisted in an NaCl- Ca-free solution. Thus, the mechanism of repetitive activity at the depolarized level appears to be related to the presence of the negative slope in the inward K+ rectifier I-V relation.
- 中文關鍵字: --
- 英文關鍵字: Inward K+ rectification; Negative slope conductance; Depolarization-induced activity; Early afterdepolarizations; Cromakalim; Barium