Abstract
1. The effects of some anions (Br, NO3, I, SCN, substituted for Cl) and cations (TEA, NH4, substituted for Na) on the membrane resistance and twitch tension of frog skeletal muscle fibres were investigated.
2. In nitrate-Ringer, both of membrane resistance and twitch tension increased in proportion to the concentration of nitrate.
3. The degrees of twitch potentiation by these anions were Cl<Br<NO3<I<SCN. The increasing factor of membrane resistance was also in the same order, the relative values were Cl:Br:NO3:I:SCN=1:1.2:1.5:1.7:2.0. But the relation between twitch tension and membrane resistance was not linear. These anions have a facilitatory action on excitation-contraction coupling, besides an increasing effect on membrane resistance.
4. The membrane resistance showed little or no change by TEA substitution, but twitch tension was potentiated far more than expected from prolonged. action potential. Therefore, TEA has the prolonging action on membrane depolarization and the facilitatory action on excitation-contraction coupling.
5. When NH4 was substituted for 20% of Na, membrane resistance as well as twitch tension showed a transient increase within several minutes, and in 10minutes both of them fell down to steady value. But in 50% NH4-Ringer, the excitation-contraction coupling was blocked in 10minutes, and tension was depressed to the value lower than 30%, despite of the prolonged action potential.
6. The two effects of these anions and cations were discussed; the one is the effect on membrane, increasing the membrane resistance, prolonging the depolarization, thus the twitch tension is indirectly potentiated, and the other is the direct effect on the excitation-contraction coupling.
