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Voltage‐clamp experiments on frog single skeletal muscle fibres: evidence for a tubular sodium current.
Author(s) -
Mandrino M
Publication year - 1977
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.1977.sp011918
Subject(s) - sodium , chemistry , biophysics , voltage clamp , current (fluid) , reversal potential , tetrodotoxin , sodium channel , sucrose gap , membrane potential , cardiac transient outward potassium current , conductance , potassium , tetraethylammonium , patch clamp , biochemistry , biology , receptor , mathematics , organic chemistry , combinatorics , electrical engineering , engineering
1. A late inward current following the initial sodium current is sometimes observed on frog single skeletal muscle fibres studied in voltage‐clamp conditions by the double sucrose‐gap method. 2. The late inward current is time and voltage dependent; it is sensitive to extracellular sodium concentration and inhibited by tetrodotoxin. Therefore, it is very probably carried by sodium ions. 3. It is assumed that the late current reflects a regenerative increase of sodium conductance in the tubular membrane. The main argument favouring this assumption is that the late current is never observed on detubulated fibres. 4. Inactivation studies show a marked difference between the evolution of the two inward currents when the membrane resting potential is increased by previous hyperpolarizations in a high range of values: the late current is decreased while the initial current remains constant. The decrease of the late current is suppressed by tetraethylammonium ions or in a potassium‐free medium. On detubulated fibres, the sodium current is never decreased by conditioning hyperpolarizations. 5. It is postulated that a fast transient potassium current, located in the bubular membrane, should develop contemporaneously with the sodium current. 6. The decay of the sodium inactivation is anaylsed on semilogarithmic plot: on normal fibres, it runs in two phases while on detubulated fibres, one phase only is found.