Abstract
Determinations have been made of the concentrations of adenosine triphosphate, adenosine diphosphate, adenylic acid, creatine phosphate and inorganic phosphate in isolated, electrically driven left atria of guinea pigs under various experimental conditions and in the presence of various drugs which produce changes in contractile strength. It has been shown that values for adenylpyrophosphate concentration (labile phosphate of ATP and ADP) obtained with either the acid-heat hydrolysis method or the potato adenylpyrophosphatase method agree closely with values obtained with the more specific Kalckar deaminase method in which ATP, ADP and AMP are determined individually.
In hypodynamic atria which had undergone spontaneous failure the mean concentrations of the high energy phosphate compounds—ATP, ADP and CP—were not significantly different from the respective mean concentrations in control atria prior to failure, or from those concentrations in atria which had been restored from failure with strophanthin-K.
Decreases in contractile strength resulting from a reduction in frequency of stimulation, addition of acetylcholine or addition of ryanodine were not associated with any significant changes in concentrations of high energy phosphate compounds from the control levels.
Increases in contractile strength resulting from the addition of non-toxic doses of strophanthin-K, of extra CaCL2 or of epinephrine in a final concentration around 10-7, were not associated with any significant changes in concentrations of high energy phosphate compounds from the control levels.
Anoxia produced a marked decrease in both contractile strength and high energy phosphate content, with the fall of CP being much greater than that of ATP. Poisoning with excess glycoside also produced both a decrease in contractile strength and a decrease in CP and ATP. Moderate decreases in these compounds also occurred in atria exposed to a low potassium medium, even though this procedure leads to an increase in contractile strength.
Epinephrine and norepinephrine in concentrations giving maximal stimulation of contractile strength (10-6 to 10-5) produced small but significant decreases in CP.
Our findings have been compared with those of previous investigators, and suggestions made to explain certain discrepancies in findings. It is concluded that marked changes in contractile strength of cardiac muscle may be produced by a variety of agents and conditions independently of any changes in the concentrations of high energy phosphate compounds.
Footnotes
- Received June 20, 1958.
- © 1958, by The Williams & Wilkins Company
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