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Existence of a sodium‐induced calcium release mechanism of frog skeletal muscle fibres.
Author(s) -
Potreau D,
Raymond G
Publication year - 1982
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1982.sp014464
Subject(s) - depolarization , biophysics , chemistry , contraction (grammar) , sodium , voltage clamp , current clamp , calcium , reversal potential , muscle contraction , resting potential , ion , membrane potential , anatomy , patch clamp , medicine , biochemistry , receptor , organic chemistry , biology
1. The electrical and the mechanical activity of isolated frog muscle fibres have been simultaneously recorded in a physiological solution which allows the development of a large tubular sodium current. 2. Under such experimental conditions, fibres develop long‐lasting action potentials and strong mechanical responses. 3. In voltage‐clamp experiments a slow inward current is revealed for depolarizations higher than +20 mV from the resting potential. This current increases until +40 to +50 mV and then decreases to reverse near +90 mV. The amplitude of the mechanical response increases with the potential to reach an optimum value between +40 and +50 mV and then decreases to stabilize when the depolarization is near +90 mV. 4. In the presence of picrotoxin the slow inward current is reversibly inhibited and the tension‐depolarization curve has an S‐shape as found in normal physiological conditions. 5. The dependence of a part of the contraction upon the slow inward current is reinforced by the fact that in a 50% sodium solution the amplitude of the current and that of the contraction are reduced in the same proportion. 6. Detubulated fibres failed to generate such a sodium inward current. 7. When sodium ions are replaced by lithium ions a slow inward lithium current develops but it does not induce a mechanical response. 8. Tetracaine reversibly inhibits the current‐dependent component of the contraction without affecting the potential‐dependent one. 9. It is concluded that the contraction recorded in the present experimental conditions is the sum of two components: one is potential‐dependent and the other depends on a sodium‐induced calcium release mechanism.