The effect of fluoride and calcium ions upon the insulin plus lactate‐stimulated K uptake and respiratory rate of frog muscles

Using paired frog muscles it was shown that fluoride caused no observable change in the rate of oxygen consumption in Ca ++ ‐free Ringer's solution, but stimulated the rate in Ca ++ ‐containing Ringer's; the obvious explanation for this stimulation is the spontaneous activity of the muscle caused by the rapid lowering of Ca ++ ion concentration when fluoride was added. Fluoride had no effect on potassium movement in these experiments. In a Ca ++ ‐free solution fluoride (0.03 M) inhibited the insulin + lactate‐stimulated oxygen consumption of muscles which had been adapted to the absence of calcium by overnight soaking. In Ca ++ ‐containing Ringer's there was no net effect of fluoride, demonstrating the fact that the direct inhibition of oxygen consumption was cancelled by the indirect stimulation caused by the fluoride‐lowering of the Ca ++ ion concentration. Fluoride depressed the IL‐induced K uptake but for this effect some calcium, albeit a very low concentration, was necessary. Fluoride did not alter the muscle glycogen concentrations. The only observable effect of calcium (in the absence of fluoride) was a rise in respiration caused by exposure to a sudden reduction in Ca ++ ion concentration. Both the IL‐stimulated O 2 rate and K uptake were independent of Ca ++ ions since they occurred in Ca ++ ‐free adapted muscles, in muscles exposed to a rapid reduction of Ca ++ ions as well as in muscles in a Ca ++ ‐containing Ringer's solution.