PMID: 6535866Jan 1, 1984Paper

Effects of divalent cations on biphasic potassium contractures and on contractile inactivation in low calcium solutions in frog single twitch muscle fibers

The Japanese Journal of Physiology
M TakaujiT Nagai

Abstract

When the concentration of external Ca2+ was reduced for 30 sec in a single twitch muscle fiber of a frog, the peak tension of the initial component of biphasic 80 mM K+ contractures was potentiated, whereas that of the secondary component was markedly inhibited, despite the fact that in the early stage it was potentiated usually in case of contractures in 60 and 40 nM K+ but rarely in 80 mM K+. These changes were not observed, however, in the presence of 0.5-1 nM Mn2+, i.e., Mn2+ having been substituted for Ca2+. The foregoing result and the authors' previously reported data indicated the following. First, the concentrations of divalent cations having an equal effect in bringing about the peak tensions of both components are 3 mM Mg2+, 0.7 mM Mn2+, 0.5 mM Ni2+, and 1.8 mM Ca2+. Secondly, this sequence constitutes their increasing order of effectiveness on the time course of the secondary component. Meanwhile, a similar order was found to exist in another experiment concerning the effectiveness in inhibiting the inactivation of K contractures facilitated by lowering the concentration of external Ca2+. All these findings indicated that the divalent cations act on the activation processes of both components in a stabilizing manner...Continue Reading

Citations

Jan 1, 1988·Clinical and Experimental Pharmacology & Physiology·Y N Singh, W F Dryden

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