PT - JOURNAL ARTICLE AU - Ira W. Hillyard AU - Leonard Procita TI - THE EFFECT OF RYANODINE ON THE CONTRACTILE STRENGTH OF MAMMALIAN CARDIAC (ATRIAL) MUSCLE DP - 1959 Sep 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 22--28 VI - 127 IP - 1 4099 - http://jpet.aspetjournals.org/content/127/1/22.short 4100 - http://jpet.aspetjournals.org/content/127/1/22.full SO - J Pharmacol Exp Ther1959 Sep 01; 127 AB - Ryanodine, a highly active alkaloid derived from the South American plant Ryania speciosa Vahl, has been investigated for its action on cardiac muscle, using isolated spontaneously beating kitten auricles. On this preparation ryanochine in concentrations as low as 5 x l0-9 M produces a progressive depression of the contractile force, terminating in almost complete, irreversible failure. There is no contracture or systolic arrest. The effect of this alkaloid is more specific for contractility since the spontaneous rhythmicity is never depressed by more than 30 to 40% at the time the contractile force is almost completely depressed. The velocity, but not the degree of the contractile failure is dependent on the ryanodine concentration used, and is significantly influenced by the level of existing rhythmical activity. The ryanodine-induced contractile failure while irreversible with respect to repeated washing, can he temporarily reversed by epinephrine or some related sympathomimetic amine or excess calcium. Some evidence is discussed which suggests that the action of ryanodine cannot be attributed to a depletion of the " high energy" phosphate compounds or to some direct physicochemical alteration of the contractile proteins.