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Origin of delayed outward ionic current in charge movement traces from frog skeletal muscle.
Author(s) -
Hui C S,
Chen W
Publication year - 1994
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.1994.sp020281
Subject(s) - movement (music) , current (fluid) , skeletal muscle , anatomy , chemistry , neuroscience , biophysics , biology , physics , acoustics , thermodynamics
1. Non‐linear membrane ionic current was studied in highly stretched cut frog twitch fibres in a double Vaseline‐gap voltage clamp chamber, with the internal solution containing 0.1 mM EGTA and the external solution containing Cl‐ as the major anion. After the Na+ currents was abolished by TTX in the external solution and the K+ currents were suppressed by external TEA+ and Rb+ and internal Cs+, a delayed outward ionic current with a time course similar to that of the delayed rectifier current was observed during depolarization. 2. The delayed outward ionic current was resistant to 1 mM 3,4‐diaminopyridine (3,4‐DAP) in the external solution and was unaltered when a fraction of the internal Cs+ was replaced by K+ or Na+, suggesting that the current was not carried by cations flowing through the delayed rectifiers. 3. The delayed outward ionic current was greatly reduced by replacing the external Cl‐ with CH3SO3‐,SO4(2‐), glutamate or gluconate, indicating strongly that the current was carried by Cl‐ flowing through anion channels. The current was also suppressed by 1 mM external 9‐anthracenecarboxylic acid (9‐ACA). 4. The delayed outward ionic current was reduced by blockers of calcium‐dependent Cl‐ channels, such as SITS and frusemide (furosemide), in a dose‐ and voltage‐dependent manner and by increasing intracellular [EGTA] to 20 mM, suggesting that part of the Cl‐ current in the muscle fibres could be calcium dependent. 5. The total Cl‐ current could be dissected into calcium‐dependent and calcium‐independent components. Each component accounted for roughly half of the total Cl‐ current. The maximum slope conductance of the calcium‐dependent Cl‐ channels was 60.9 +/‐ 6.0 microS microF‐1 (mean +/‐ S.E.M., n = 4).