Effects of some divalent cations on frog twitch muscles

Publisher Website
Google Scholar
Abstract
Measurements were made of the peak tension of and the area under the contractures of the frog toe muscles which were provoked by various concentrations of potassium. The replacement of Ca by equivalent amounts of various divalent ions was found to have the following effects: in the presence of 5 mM Mg and Sr the area under the contracture curves and the mechanical threshold were decreased, i.e., these 2 ions acted like Ca at a lower concentration. Ni, Co, and Mn increased the threshold and the size of the contractures, i.e., they acted like a higher Ca concentration. Cd reduced the Zn (1 mM) did not change the threshold, but they both increased the area under the contracture curve. The Ca45 bound to the preparations of the sarcoplasmic reticulum of frog muscle was partly released following the addition of Cd and Zn; Ni and Mn as well as NO3 were without effect. The resting release of Ca45 from intact frog toe muscles was decreased by Co, Zn, and Cd. The washout of the self-exchangeable fraction of Ca45 bound to the muscle was an order of magnitude slower in the presence of Co or Mn than in the presence of Ca40. The rate coefficient of the Ca45 release was transiently increased by about 5 times when 120 mM K was applied in the presence of both Ca and Co.