RT Journal Article SR Electronic T1 ABSENCE OF EFFECTS OF CARDIAC GLYCOSIDES ON CARDIAC MYOSIN AND A Ca++-SENSITIVE RECONSTITUTED CARDIAC ACTOMYOSIN JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 558 OP 565 VO 154 IS 3 A1 Arnold M. Katz YR 1966 UL http://jpet.aspetjournals.org/content/154/3/558.abstract AB Ouabain in concentrations from 10-4 to 10-10 M had no effect upon either the Mg++- or Ca++-activated adenosine triphosphatase activity of cardiac myosin. Examination of a reconstituted cardiac actomyosin which responds to physiologic variations of free Ca++ concentration revealed no stimulatory effects of ouabain on either adenosine triphosphatase activity or superprecipitation. No evidence was obtained that ouabain potentiates the stimulatory action of free Ca++ or exerts a direct Ca++-like action on actomyosin. Similarly, digitoxin was without effect on these in vitro systems. The positive inotropic action of cardiac glycosides on the intact heart thus does not appear to reflect a direct interaction with the contractile proteins. © 1966 by The Williams & Wilkins Co.