RT Journal Article
SR Electronic
T1 PHOSPHORYLASE ACTIVITY OF HEART MUSCLE UNDER VARIOUS CONDITIONS AFFECTING FORCE OF CONTRACTION
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 257
OP 264
VO 127
IS 4
A1 Julius Belford
A1 Marcia R. Feinleib
YR 1959
UL http://jpet.aspetjournals.org/content/127/4/257.abstract
AB Phosphorylase activity was determined in a variety of experimental conditions affecting force of contraction of cardiac muscle. In the isolated guinea pig auricle calcium and K-strophanthin increased the per cent of phosphorylase a concomitant with their positive inotropic actions. However, excess concentrations of these agents which depressed force of contraction also gave rise to increased levels of phosphorylase a. A 3-hour period of 1 per second stimulation which produced no overt contractile depression in the isolated guinea pig auricle, lowered the per cent of phosphorylase a. Epinephrine increased force of contraction as well as the per cent of phosphorylase a in the isolated rat auricle. Depression of the isolated rat auricle with anoxia, quinidine or pentobarbital did not result in any significant change in phosphorylase a. "Failure" induced by prolonged high frequency stimulation of the isolated rat auricle resulted in significant lowering in per cent phosphorylase a. "Failure" induced in the intact cat by similar stimulation also produced a significant decline in per cent of ventricular phosphorylase a. Hemorrhagic hypotension in the intact cat did not alter ventricular phosphorylase a content. In the intact cat, digitoxin in sufficiently high doses to produce arrythmia did not significantly affect phosphorylase a activity. On the basis of all findings we conclude that, although in certain instances there may appear to be a parallelism between phosphorylase a activity and contractile force, a direct relationship does not obtain in all cases.