- 作者: Daniel E. Berg; Mario Vassalle
- 作者服務機構: Department of Physiology and Pharmacology, State University of New York, Health Science Center, Brooklyn, N.Y., USA
- 中文摘要: --
- 英文摘要: The mechanisms by which low [K+]o induces sponta-neous activity was studied in sheep Purkinje fibers. Pur-kinje strands were superfused in vitro and membranepotentials were recorded by means of a microelectrodetechnique. The results show that low [K+]o increases theslope and amplitude of early diastolic depolarization,sharpens the transition between early and late diastolicdepolarizations, induces an after-potential and large pre-potentials through a negative shift of an oscillatory zone.Pre-potentials occur progressively sooner during dias-tole and merge with the after-potential to induce uninter-rupted spontaneous discharge. During recovery, whenthe rate slows, after- and pre-potentials separate oncemore, the slower discharge decreasing the after-poten-tials but not the pre-potentials. Low [K+]o has little effecton the plateau, but markedly slows phase 3 repolariza-tion and may altogether prevent it. At depolarized levels,voltage oscillations, slow responses, sinusoidal fluctua-tions or quiescence may be present depending on volt-age. During the recovery, a train of either sub-thresholdoscillations or spontaneous action potentials appear to-wards the end of phase 3 repolarization. The cessation ofthe action potentials unmasks large sub-threshold oscil-lations, that occur in the oscillatory zone. Drive, high[Ca2+]o and norepinephrine increase slope and amplitudeof early diastolic depolarization as low [K+]o does. In low[K+]o, Cs+ prevents spontaneous discharge at polarizedlevels, but not the decrease in resting potential nor theonset of slow responses at depolarized levels. Cs+ blocksthe train of oscillations and of action potentials occurringduring recovery. We conclude that low [K+]o steepensearly diastolic depolarization and increases its amplitudethrough an after-potential that results from an increasedCa2+ load; allowsthe attainment of the threshold throughCs+-sensitive voltage oscillations which develop whenthe oscillatory zone is entered either by diastolic depolar-ization or by phase 3 repolarization; and causes voltageoscillations also at depolarized levels, but through a Cs+-insensitive different mechanism.
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- 英文關鍵字: --