The voltage-dependent blocking effect of phalloidin on the delayed potassium current of voltage-clamped frog skeletal muscle fibres

Phalloidin, like the later-detected phallotoxins, consists of a cyclic heptapeptide backbone, the ring being crosslinked by a 2'-indolylthioether moiety (tryptathionine). After intraperitoneal administration--not per os--it will, after a short time, damage the liver specifically, presumably in consequence of its very tight binding to F-actin preventing its dissociation. This affinity can be utilized for a sensitive visual identification of F-actin by using fluorescent derivatives.

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The apamin-sensitive potassium current in frog skeletal muscle: its dependence on the extracellular calcium and sensitivity to calcium channel blockers

Traoré

Cognard

Potreau

et al. 1986

Pflugers Arch.

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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.

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The voltage-dependent blocking effect of phalloidin on the delayed potassium current of voltage-clamped frog skeletal muscle fibres

Cited by 6 publications

References 28 publications

Potassium Channel Toxins

Potassium Channel Toxins

50 Jahre Phalloidin

The apamin-sensitive potassium current in frog skeletal muscle: its dependence on the extracellular calcium and sensitivity to calcium channel blockers

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