The correlation between the increase in slow outward current and in contraction induced by caffeine, ryanodine, and rapid cooling in voltage-clamped frog muscle fibers
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Published:1991-06-01
Issue:6
Volume:69
Page:859-864
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ISSN:0008-4212
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Container-title:Canadian Journal of Physiology and Pharmacology
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language:en
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Short-container-title:Can. J. Physiol. Pharmacol.
Author:
Nasri-Sebdani Mohammad,Traoré Flavien,Mouzou Aklesso,Cognard Christian,Potreau Daniel,Raymond Guy
Abstract
The effects of caffeine, ryanodine, and rapid cooling were tested on the depolarization-induced contraction and the apamin-insensitive slow outward current (Iso) of voltage-clamped (double mannitol gap) single frog muscle fibers. Subthreshold caffeine concentrations (0.5–2 mM) induced a monotonic increase in contractile and Iso amplitude. Whatever the concentration, the increase in contraction was roughly twice the one in current. Similar results were obtained upon rapid cooling (20–4 °C) in the presence of 0.5 mM caffeine. In the absence of external Na+ (choline-substituted) 10−5 M ryanodine induced a delayed increase (≈30 min) in contraction and in current, shortly before the development of a drastic and irreversible contracture. Here again, the increase in contraction was twice that in current. In the presence of 5 mM tetraethylammonium (TEA) and (or) 25 nM charybdotoxin, 2 mM caffeine still induced a strong facilitating effect on contraction but the parallel increase in current was strongly reduced. The linear relationship between the increase in current and contractile amplitude has a slope ≈0.5 (whatever the drug used to increase contractility); it is ≈0.1 in the presence of TEA and (or) charybdotoxin. In conclusion, provided the changes in contractile amplitude are caused by parallel changes in depolarization-induced sarcoplasmic reticulum Ca2+ release, about 50% of the apamin-insensitive Iso is controlled by internal Ca2+ release. The main part of this current corresponds to the TEA- and charybdotoxin-sensitive component of Iso.Key words: skeletal muscle, voltage clamp, Ca2+-dependent K+ current, sarcoplasmic reticulum calcium release, caffeine, ryanodine, charybdotoxin.
Publisher
Canadian Science Publishing
Subject
Physiology (medical),Pharmacology,General Medicine,Physiology
Cited by
1 articles.
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