Electrical properties of white and red muscle fibres of the elasmobranch fish Scyliorhinus canicula.

1. Standard electrophysiological techniques (including a method which controls the membrane potential at a point on a muscle fibre) were used to investigate the electrical properties of white and red muscle fibres of the elasmobranch fish Scyliorhinus canicula.2. The resting potential of the white fibres in the standard Ringer solution was - 85.2 +/- 0.4 mV. That of the red fibres was - 71.1 +/- 1.2 mV. The membrane resistance of white fibres was 1588 +/- 97 Omega cm(2) and that of red fibres was 5410 +/- 1070 Omega cm(2).3. White fibres always responded to direct stimulation with an action potential. It proved impossible, with two impaling micro-electrodes, to record action potentials from the red fibres, although on one occasion an abortive spike was seen.4. The resting membrane of the red fibres seemed less permeable to chloride than was the membrane of the white fibres. However, the resting potassium permeability showed the potential dependence called inward or anomalous rectification in both white and red fibres.5. White fibres responded to square depolarizing pulses with conductance changes to sodium and, subsequently, to potassium.6. All red fibres examined with the point voltage clamp showed a delayed increase in potassium conductance on depolarizing.7. Out of twenty-seven red fibres examined, six showed no sign of having any sodium conductance mechanism. Eight showed large sodium currents on depolarizing, and the remaining thirteen had small sodium currents. It seemed likely that the group of eight fibres might be able to propagate action potentials.