THE EFFECTS OF SUGAR AND ELECTROLYTE SOLUTIONS ON THE METABOLISM AND IRRITABILITY OF HEART MUSCLE

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Abstract
Experiments in vitro on the frog''s heart showed that isotonic solns. of KC1 and sucrose depress the O2 consumption of irritable or non-irritable cardiac muscle. This is associated with a decrease in muscle tone and loss of irritability. Isotonic CaCl2 increases both the tone and metabolic rate of irritable and non-irritable heart muscle, but renders the irritable muscle non-irritable. The antagonistic action of KC1 and sucrose and of CaCl2 on the metabolic rate and tone of heart muscle is found to be opposite that on irritable skeletal muscle. Furthermore, the action of these substances is independent of the previous state of irritability of heart muscle but varies with the previous state of irritability of skeletal muscle. If spontaneous sugar or K non-irritability in cardiac muscle is due to the same causes as obtain in skeletal muscle, the similarity of the action of sucrose and K solns. may be due to the washing away of Ca by the sucrose soln. and thus to increase in the K/Ca ratio at the surface membranes of the muscle fibers. Furthermore, if the differences observed are due to membrane equilibria, it may be suggested that heart muscle differs from skeletal muscle in having its membranes reversed and that a similar reversal of equilibrium is responsible for the phenomenon of non-irritability in skeletal muscle. Much more study, however, is required before theorizing in these matters will be profitable. The metabolic rate of non-irritable cardiac muscle first decreases, then after several hrs. increases, and finally returns to normal after immersion in an isotonic soln. of glucose. Ringer''s soln. slightly depresses O2 consumption of spontaneously non-irritable cardiac muscle, but has no effect on the metabolic rate of irritable heart muscle. HC1 in concn. above 0.01 M in isotonic NaCl decreases O2 consumption of spontaneously non-irritable heart muscle. Methylene blue increases O2 consumption of irritable and non-irritable heart muscle.

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