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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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+×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.
Key wordsCa2+-dependent K+ permeability Ca2+-channel blockers Apamin Voltage-clamp Skeletal muscle
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- Adrian RH, Chandler WK, Hodgkin AL (1970) Slow changes in potassium permeability in skeletal muscle. J Physiol (Lond) 208:645–668Google Scholar
- Almers W, Palade PT (1981) Slow calcium and potassium currents across frog muscle membrane: measurement with a vaseline gap technique. J Physiol (Lond) 312:159–176Google Scholar
- Armstrong CM, Bezanilla F, Horowicz P (1972) Twitches in the presence of ethylene glycol bis-(amino-ethylether)-N,N′-tetraacetic acid. Biochem Biophys Acta 267:605–608Google Scholar
- Bezanilla F, Caputo C, Horowicz P (1971) Voltage clamp activation of contraction in short striated muscle fibers of the frog. Acta Cient Venz 22:72–74Google Scholar
- Bkaily G, Sperelakis N, Renaud JF, Payet MD (1985) Apamin, a high specific Ca2+ blocking agent in heart muscle. Am J Physiol 248:H961-H965Google Scholar
- Burgess GM, Claret M, Jenkinson DH (1981) Effects of quinine and apamin on the calcium dependent potassium permeability of mammalian hepatocytes and red cells. J Physiol (Lond) 317:67–90Google Scholar
- Caputo C, Bezanilla F, Horowicz P (1984) Depolarization contraction in short striated muscle fibers. A voltage-clamp study. J Gen Physiol 84:133–154Google Scholar
- Cognard C, Traoré F, Potreau D, Raymond G (1984) Effects of apamin on the outward potassium current of isolated frog skeletal muscle fibres. Pflügers Arch 402:222–224Google Scholar
- Cognard C, Ewané-Nyambi G, Potreau D, Raymond G (1986a) The voltage-dependent blocking effect of phalloidin on the delayed potassium current of voltage-clamped frog skeletal muscle fibres. Eur J Pharmacol 120:209–216Google Scholar
- Cognard C, Lazdunski M, Romey G (1986b) Contribution of the apamin-sensitive Ca2+-activated K+ current in the “apparent” inactivation of the Ca2+ current in mammalian skeletal muscle. J Physiol (Lond) 371:263PGoogle Scholar
- Cook NS, Haylett DG (1985) Effects of apamin, quinine, and neuromuscular blockers on calcium activated potassium channels in guinea-pig hepatocytes. J Physiol (Lond) 358:373–394Google Scholar
- Dörrscheidt-Käfer M (1977) The action of D-600 on frog skeletal muscle: facilitation of excitation-contraction coupling. Pflügers Arch 369:259–267Google Scholar
- Eisenberg RS, Howell JN, Vaughan PC (1971) The maintenance of resting potential in glycerol-treated muscle fibres. J Physiol (Lond) 215:95–102Google Scholar
- Fink R, Lüttgau HCh (1976) An evaluation of the membrane constants and the potassium conductance in metabolically exhausted muscle fibres. J Physiol (Lond) 263:215–238Google Scholar
- Fink R, Hase J, Lüttgau HCh, Wettwer E (1983) The effect of cellular energy reserves and internal calcium ions on the potassium conductance in skeletal muscle of the frog. J Physiol (Lond) 336:211–228Google Scholar
- Frank GB (1982) Roles of extracellular and “trigger” calcium ions in excitation-contraction coupling in skeletal muscle. Can J Physiol Pharmacol 60:427–439Google Scholar
- Gage PW, Eisenberg RS (1969) Action potentials, after potentials and excitation contraction coupling in frog sartorius fibres without transverse tubules. J Gen Physiol 53:298–310Google Scholar
- Habermann E (1972) Bee and wasp venoms. Science 177:314–322Google Scholar
- Habermann E (1984) Apamin. Pharmacol Ther 25:255–270Google Scholar
- Howell JN, Jenden DJ (1967) T. Tubules of skeletal muscle: morphological alterations which interrupt excitation-contraction coupling. Fed Proc 26:553Google Scholar
- Hugues M, Romey G, Duval D, Vincent JP, Lazdunski M (1982a) Apamin as a selective blocker of the calcium-dependent potasium channel in neuroblastoma cells: voltage-clamp and biochemical characterization of the toxin receptor. Proc Natl Acad Sci USA 79:1308–1312Google Scholar
- Hugues M, Schmid H, Romey G, Duval D, Frelin Ch, Lazdunski M (1982b) The Ca2+-dependent slow K+ conductances in cultured rat muscle cells: characterization with apamin. EMBO J 1:1039–1042Google Scholar
- Kirsch GE, Nichols RA, Nakajima S (1977) Delayed rectification in the transverse tubules. Origin of the late after-potential in frog muscle. J Gen Physiol 70:1–21Google Scholar
- Maruyama Y, Gallacher DV, Petersen QH (1983) Voltage and Ca2+-activated K+ channels in baso-lateral acinar cell membranes of mammalian salivary glands. Nature 302:827–829Google Scholar
- Palade PT, Almers W (1985) Slow calcium and potassium currents in frog skeletal muscle: their relationship and pharmacologic properties. Pflügers Arch 405:91–101Google Scholar
- Potreau D, Raymond G (1980) Slow inward barium current and contraction on frog single muscle fibres. J Physiol (Lond) 303:91–109Google Scholar
- Potreau D, Raymond G (1982) Existence of a sodium-induced calcium release mechanism on frog skeletal muscle fibres. J Physiol (Lond) 333:463–480Google Scholar
- Raymond G, Potreau D (1977) Barium ions and excitation-contraction coupling of frog single muscle fibres under controlled current and voltage. J Physiol (Paris) 73:617–631Google Scholar
- Romey G, Lazdunski M (1984) The coexistence in rat muscle cells of two distinct classes of Ca2+-dependent K+ channels with different pharmacological properties and different physiological functions. Biochem Biophys Res Commun 118:669–674Google Scholar
- Romey G, Hugues M, Schmid-Antomarchi H, Lazdunski M (1984) Apamin: a specific toxin to study a class of Ca2+-dependent K+ channels. J Physiol (Paris) 79:259–264Google Scholar
- Sanchez JA, Stefani E (1978) Inward calcium current in twitch muscle fibres of the frog. J Physiol (Lond) 283:197–209Google Scholar
- Seagar M, Granier C, Couraud F (1984) Interactions of the neurotoxin apamin with a Ca2+-activated K+ channels in primary neuronal cultures. J Biol Chem 259:1491–1496Google Scholar
- Stanfield PR (1970) The effect of tetraethylammonium ion on the delayed currents of frog skeletal muscle. J Physiol (Lond) 209:209–229Google Scholar