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KMID : 0377519960210020151
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Chung-Ang Journal of Medicine
1996 Volume.21 No. 2 p.151 ~ p.168
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The Effect of Extracellular pH on Outward K+ Currents in Rabbit Portal Vein Myocytes
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Abstract
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Single smooth muscle cells isolated from rabbit protal vein were voltage-clamped at room temperature using the whole cell configuration of the patch clamp technique. Outward current elicited upon depolarization from -60 mV could be divided into
two
components, an non-inactivating highly oscillating current and an inactivating less oscillating current. Non-inactivating current was evoked by depolarizing voltage pulses from a holding potential of -60 mV when low EGTA K+-internal
solution(EGTA=5
mM,
pCa 7.0) was in the micropipettes. The outward current exhibited properties of voltage-dependency but did not inactivate significantly over 8 sex. Some cells showed the characteristics of spontaneous transient outward currents (STOCs). The
outward
current was sensitive to tetraethylammonium(TEA) and external calcium but not to 4-aminopyridine(4-AP).
Changes in external pH strongly affected the amplitude of the outward K+ currents. Increasing external pH from 7.4 to 7.9 increased the outward K+ current but more alkalinization to 8.4 decreased the outward current than the control current.
Time-dependent inactivating K+ current activated when the pipette solution contained 10 mM EGEA with no calcium. The relatively smooth outward current showed voltage-dependency and time-dependent inactivation. It was blocked by 4-AP(2 mM), but
not
by
extracellular calcium change. Alkalinization to 8.4 reduced the outward K+currents elicited when K+-internal solution with high EGTA was used in the micropipette.
From these results, Ca2+activated K+ current and delayed rectifier K+ current in the smooth muscle cells of rabbit portal vein were identified. The mechanism of regulation of vascular tone by alteration of extracellular pH could be accounted for
by
the
modulation of two types of outward K+ currents.
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KEYWORD
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