ACTIONS OF SOME ANIONS ON ELECTRICAL PROPERTIES AND MECHANICAL THRESHOLD OF FROG TWITCH MUSCLE

1. Using two micro‐electrodes in a point‐voltage clamp technique, the effects of the lyotropic anions, NO3μ−, Brμ−, Iμ−, SCNμ−, and CH3SO4μ−, and of SO42− on the mechanical threshold and electrical properties of frog sartorius muscle were studied. 2. In chloride Ringer solution the spike threshold was ‐59 mV, mechanical threshold ‐48 mV, and the threshold for delayed rectification of the total current at about 100 msec −52 mV. 3. When Clμ− was replaced by one of the lyotropic anions, the effective resistance determined at ‐100 mV tended to increase. But, because of the variability of the effective resistance in individual fibres, most lyotropic anions did not cause a statistically significant increase in the effective resistance. Only Iμ− and SO42− significantly increased the effective resistance. 4. Most lyotropic anions had no significant effect on the spike threshold; Iμ−, at 58 m M, lowered it slightly. Sulphate raised the threshold. 5. Tetrodotoxin (0·1 μg/ml.) abolished the spikes, but did not affect the mechanical and delayed rectification thresholds. It was, therefore, used to pre‐treat all preparations for determining these thresholds. 6. All lyotropic anions lowered the mechanical and the delayed rectification thresholds, the order of effectiveness being approximately SCNμ− > Iμ− > NO3μ− > CH3SO4μ− > Brμ−. As in Clμ− Ringer, the two thresholds lay very close together in every case. Sulphate raised slightly both the mechanical and delayed rectification thresholds, again in close parallel. 7. This close agreement of the mechanical and delayed rectification thresholds is not caused by movement artifact, because in fibres in which visible contractions were eliminated with hypertonic solutions the delayed rectification thresholds were the same as those in contracting fibres. 8. In spite of the close agreement, reasons are given to doubt a direct causal relationship between the mechanical and delayed rectification thresholds. 9. Nitrate apparently had little effect on the rate of inactivation of the outward current, or on the relation between steady‐state inactivation and membrane potential. © 1968 The Physiological Society