BIOPHYSICAL AND MECHANICAL PROPERTIES OF RED AND WHITE MUSCLE FIBRES IN FISH

1. The electrical properties of red muscle fibres of the silver carp (Carassius auratus (Linné)) were investigated and compared with those of white fibres. The resting membrane potential of red muscle was −73·1 mV, and of white muscle −82·4 mV. The effective resistance of fibre, time constant and space constant were 1·43 MΩ, 26·6 msec and 2·1 mm for red muscle and 1·0 MΩ, 48·4 msec and 1·9 mm for white muscle. 2. The membrane capacitance in red muscle was 2·55 μF/cm2 and in white muscle was 7·23 μF/cm2, though the sarcoplasmic reticulum and the transverse tubular system were developed equally in both tissues. 3. No rectification could be observed in the current—voltage relation in both the muscles. However, in excess potassium solutions, both types of muscle showed anomalous rectification. 4. In red muscle it was rare to trigger a spike by nerve stimulation or by field stimulation of the tissue. However, in white muscle, there appeared graded responses and occasionally spikes were generated with overshoot potentials. 5. Excess potassium concentration produced contracture in the red muscle, but even forty times of normal potassium never produced contracture in the white muscle. © 1969 The Physiological Society