The Effect of Sodium Ions on Resting and Action Potentials in Skeletal Muscle Fibres of Bombyx Mori (L.)

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Abstract
Sodium ions have been found to affect both the resting and action potentials of Bombyx mori muscle fibres, but the effect on the action potential is much smaller than that reported in other excitable tissues. External sodium had only a small effect on the intracellular muscle sodium, and no correlation was observed between the action potential overshoot and the theoretical ENa. The sodium ion distribution in Bombyx mori is unusual since the ratio Na0/Nai is less than unity up to 15 mM/1 external sodium. It is suggested that the muscle fibre membrane is not very permeable to sodium ions, and that on a scheme of passive diffusion alone, sodium ions could make no contribution to the inward current of the action potential.