抄録
1. A sudden increase of the external potassium concentration, [K] 0, from 5 to 80.7 mM-K caused a retractor pharynx muscle (RPM) of the snail to develop a tension of about 2.5 kg/cm2 related to log [K] 0 by a steep S-shape curve.
2. The potassium contracture tension of the muscle was reduced and eventually eliminated when the muscle was kept in calcium-free solution. The time course for this inhibition was determined by the rate that calcium ions diffuse out from the extracellular space of the muscle to bathing fluid.
3. Calcium concentration in Ringer's solution affected the magnitude of contractile response, not only contracture tension produced by potassium but also twitch tension elicited directly or indirectly; the response increased up to about 13.1 mM-Ca and decreased with a further increase in concentration.
4. Calcium and sodium affected the twitch tension of the muscle produced by direct and indirect stimulations in an antagonistic way and the tension was related to the ratio [Ca2+]:[Na+] 2 in the range of 3-20×10-4 mM-1, but the relation could not be observed on the contracture tension produced by potassium.
