The effect of diameter on the electrical constants of frog skeletal muscle fibres.

1. Electrical constants were determined on isolated single fibres or on fibres from bundles from frog's twitch muscles by analysing the low frequency cable properties.2. The sarcoplasmic conductivity (G(i)) was 5.9 mmho/cm at 20 degrees C, and its temperature coefficient (Q(10)) was 1.37.3. The Q(10) of the membrane conductance (G(M)) was 1.49, and that of the membrane capacity (C(M)) was 1.02.4. C(M) increases with diameter (D) in an approximately linear manner: the values were 4.6 muF/cm(2) at D = 50 mu, and 8.5 muF/cm(2) at D = 130 mu.5. G(M) also increases with diameter, being 0.21 mmho/cm(2) at D = 50 mu and 0.37 mmho/cm(2) at D = 130 mu.6. These results suggest that the transverse tubular system contributes substantially to the values of low frequency capacity and conductance measured at the surface membrane.