Biochemical changes accompanying enhanced cardiac contractility by ionophore XXXX .

@entity268 @entity6708 @entity141 @entity840 @entity8262 @entity1919 @entity1391 @entity3302 @entity460 @entity3365 @entity3044
We have reported that the divalent cation ionophore @entity3365 , like the beta-adrenergic agonist @entity3044 , increased the force of contraction and rate of relaxation and shortened the duration of contraction of papillary muscles isolated from @entity840 . @entity3365 produced a fall in resting tension and decreased the contracture tension of K +/- depolarized muscles, as did @entity3044 . In the present studies, @entity3044 produced a concentration-dependent, rapid, and sustained increase in the @entity1919 ( @entity268 ) content of papillary muscle. In contrast, @entity3365 had no detectable effect on @entity268 levels, even in the presence of the phosphodiesterase inhibitor, @entity3302 . Neither drug, at concentrations maximal for contractile effects, altered @entity8262 ( @entity6708 ). @entity3044 increased the @entity268 -dependent protein kinase activity ratio, whereas @entity3365 did not change the activity of this enzyme. However, both @entity3365 and @entity3044 produced a concentration-dependent increase in phosphorylase activity. Concentrations of @entity3365 or @entity3044 that enhanced contractility maximally increased the alkali-labile @entity1391 (by ca. 35%) but were without effect on the acid-labile, alkali-stable @entity1391 in the total acid precipitable protein. Contractile effects of @entity3044 , which reflect activated @entity141 uptake, and the increase in phosphorylase activity produced by this agent are believed to be due to an increase in @entity268 with subsequent activation of @entity268 -dependent protein kinases and phosphorylation of proteins. @entity3365 may produce similar contractile effects without an increase in @entity268 or @entity268 -dependent protein kinase activity by activating other protein kinases and/or inhibiting phosphoprotein phosphatases, most likely by its effects on intracellular @entity460 .
