- 作者: Hengtao Zhang; Mario Vassalle
- 作者服務機構: Department of Physioglogy and Pharmacology, State University of New York, Health Science Center, Brooklyn, N.Y., USA
- 中文摘要: --
- 英文摘要: We investigated whether in the sinoatrial node (SAN)there are two different pacemaker mechanisms andwhether either one can maintain spontaneous discharge.These questions were studied by means of an electro-physiological technique and of blockers of different dia-stolic currents in rabbit and guinea pig isolated SAN. InSAN subsidiary pacemakers of both species, Cs+ (5-10 mM) or high[K+] (10-12 mM) decreased the maxi-mum diastolic potential, abolished diastolic depolariza-tion (DD) at polarized levels (subsidiary DD), unmasked aU-shaped dominant DD at depolarized levels, but did notstop the SAN. In rabbit SAN, E4031 (1μM) and d-sotalol(100μM) did not stop discharge, but did so after block ofsubsidiary DD by high [K+] or Cs+. In guinea pig SAN, inTyrode solution E4031, d-sotalol or indapamide (100μM)did not stop SAN discharge. In the presence of Cs+or high [K+] indapamide (but not E4031 or d-sotalol)stopped the SAN. Ba (1-5 mM) led to stoppage of dis-charge both in Tyrode solution and in high [K+] or Cs+.Depolarization by blockers of DD unmasked sinusoidalfluctuations, which during recovery were responsible forresumption of discharge. We conclude that in rabbit andguinea pig SAN, two different pacemaker mechanisms(Cs+- and K+-sensitive subsidiary DD, and Cs- and K+-insensitive dominant DD) can independently sustain dis-charge, but block of both mechanisms leads to quies-cence. Abolition of dominant DD by blockers of I is con-sistent with a decay of I as the dominant pacemakingmechanism, I being more important in rabbit and I inguinea pig. Sinusoidal fluctuations appear to be anessential component of the pacemaking process.
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