The apamin-sensitive potassium current in frog skeletal muscle: its dependence on the extracellular calcium and sensitivity to calcium channel blockers.
Кључне речи
Апстрактан
Slow outward potassium currents were recorded in isolated frog skeletal muscle fibres using the double mannitol-gap voltage-clamp technique. Detubulated fibres failed to generate a slow outward current, and apamin had no effect on the remaining current. The maximum blocking effect of organic and inorganic Ca2+-channel blockers on the slow outward channels of intact fibres was larger than that of apamin. Apamin failed to induce an additional block when applied after Ca2+-channel blockers. In a low-Ca2+ solution (OCa, EGTA 1 mM) the slow outward current was slightly increased and the blocking effect of apamin was enhanced. A Ca2+-rich solution (Ca2+ X 10) increased the slow outward current and the blocking effect of apamin was drastically reduced. It is concluded that the apamin-sensitive current which is a component of the slow outward K+ current is located in the tubular membrane. Its activation seems barely dependent on the Ca2+ influx via the slow inward Ca2+ current. Apamin-receptor binding appears to be dependent on the extracellular Ca2+ concentration. Blockade of slow outward current by Ca2+-channel blockers is likely to be the result of a direct action on the slow K+ permeability rather than a consequence of Ca2+ channel inhibition.