The effect of electrolytes on the respiration of pigeon breast muscle

IT is known from the work of Stare & Baumann [1936], Greville [1937], Elliott & Elliott [1939], Elsden [1939], and Krebs & Eggleston [1940], that minced animal tissues respire best in a medium containing Na, K, Mg, Cl and P04 ions, but no Ca ions.A medium used in this laboratory, in which the above ions are present in approximately optimal concentrations, contains 0O158M Na, 0*00452M K, 0-00113M Mg, 0-122M Cl, and 0-022M P04.In experiments in which the effect of varying concentrations of Mg on the respiration of muscle tissue was studied, it was found that the optimal concen- tration of Mg is not constant, but depends on other factors, especially on the concentration of K. Furthermore the optimal concentration of K is not fixed; it is lowered by Mg.Methods The manometric experiments were carried out in conical cups.Unless other- wise stated, 3 ml. of a muscle suspension, prepared from 4 g.minced pigeon breast muscle and 45 ml.medium, were measured into the cup and the volume brought to 4 ml.by addition of substrate, electrolytes and water.Fumarate was used as a substrate.The final suspension in the cup always contained 1 part of muscle in 15 parts of medium.The centre cup contained 0-2 ml.2N NaOH.