Abstract
1. The relationship between electrical and mechanical properties of the antrum circular muscle of the guinea-pig stomach in various ionic environments was investigated by the double sucrose gap method.
2. The minimum latency was 82 msec for the onset of the contraction after the spike showed the maximum velocity of the upstroke at 38°C.
3. The slow wave, the depolarization of the membrane by excess K ion, and the electrotonic potential also produced contraction.
4. On replacement of Na ion by other substances (Li ion, tris ion and sucrose), the amplitude of the spike was similar to that elicited in the presence of Na ion. The amplitude of contraction was not reduced by tris ion, but it was reduced by sucrose and Li ion.
5. NO3 and Br ion lowered the electrical and mechanical threshold, and repetitive or enlarged spikes were evoked. The membrane resistance was reduced and the membrane was hyperpolarized. The contraction was enlarged in amplitude and prolonged in duration. Br ion showed more dominant effects on the electrical and mechanical activity than NO3 ion.
6. In the absence of Ca ion, Sr and Ba ion produced a spike with amplitude similar to that in the presence of Ca ion. However, the contraction was reduced in amplitude to a tenth of that in Krebs. When Cl ion was replaced with either NO3 or Br ion, the amplitude of contraction was restored to more than half of the control.
7. The results are discussed in comparison with the properties of skeletal muscle, and it is proposed that the Ca ion which flows into the cells as the current carrier may release at least a portion of the Ca ion bound in the membrane and activate the contractile protein. Mobilization of bound Ca ion might be influenced by Na and Cl ion.
