Spread of the Junction Potential in the T-System in Hagfish Slow Muscle Fibres

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Abstract
The membrane constants of the slow muscle fibers from the Atlantic hagfish (Myxine glutinosa) were determined by analyzing the responses to sinusoidal currents at different frequencies. The apparent low frequency membrane resistance was 20-50 k.OMEGA. .cntdot. cm2 and was not significantly altered by replacing external chloride with methyl sulfate. The low frequency capacitance was 2.1-2.4 .mu.F(farads)/cm2 and decreased to about 1 .mu.F/cm2 at 100 Hz. A model of the transverse tubular (T)-system consisting of a number unbranched T-tubules was fitted to the impedance locus. About 15 tubules/sarcomere with a length approximately 8 times the fiber radius gave good fit to the observed impedance locus. The electrical characteristics of the T-system allow an efficient electrotonic spread of the junction potential through the fiber cross-section.