The depressing effect of tetracaine and ryanodine on the slow outward current correlated with that of contraction in voltage-clamped frog muscle fibres.
The effects of tetracaine (10-50 microM) and ryanodine (0.1-10 microM) were tested on the slow outward K+ current (Iso) and the mechanical tension of isolated frog muscle fibres in a voltage-clamp device (double mannitol-gap) connected to a mechanoelectric transducer. In the concentration range tested, both drugs induced a simultaneous inhibition of tension and current. In all cases the effect on tension was twice that on current. The tetracaine-induced current and tension blocks were fully reversible and dose-dependent. In contrast the ryanodine effects on current and tension were not reversible and did not exhibit a dose dependence except for the delay before the onset of the response, which was shortened when the concentration was raised. Linear regression analysis of the time-dependent and dose-dependent effects of both drugs indicated a strong correlation between the decreases in tension and current. It is concluded that the slow outward current is partly under the control of the Ca2+ release from sarcoplasmic reticulum during contraction.
Nasri-Sebdani
M
M
Laboratory of General Physiology, URA CNRS 290, Faculty of Sciences, Poitiers, France.
Traoré
F
F
Cognard
C
C
Potreau
D
D
Poindessault
J P
JP
Raymond
G
G
D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D008564:Membrane Potentials; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D011895:Rana ridibunda; D012044:Regression Analysis; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013748:Tetracaine / Q000494:pharmacology*
D000470:Alkaloids; D013748:Tetracaine; D012433:Ryanodine; D001030:Apamin; D002118:Calcium