Function and energy metabolism of isolated rats hearts as influenced by Sr++

Effects of Sr++ and isoproterenol were studied in rat hearts perfused with red cell containing media. Sr++ in the presence of Ca++ causes a positive inotropic effect without corresponding metabolic changes. Without Ca++ 0.5 mM Sr++ causes an immediate arrest, 2 mM Sr++ a complete contracture (14 min) and 5 mM a contracture after about 44 min. At a level of 10 mM Sr++ phasic contractions are maintained (60 min). Occurring phasic contractions are prolonged 3 to 6fold. Administration of isoproterenol (ISO) at a level of 0.5 mM Sr++ causes a delayed occurrence of cardiac arrest and incomplete contracture. At a concentration of 2 and 5 mM Sr++ positive inotropic responses proceed to a contracture (7 min, 50 min resp.). VO2 is reduced by 0.5 mM Sr++ initially by 2 mM Sr++ with delay. 5 and 10 mM Sr++ induce an initial increase. Subsequent decrease is smallest at 10 mM Sr++ ISO at all Sr++ concentrations induces an increase in VO2 initially and strong reduction finally. During 10 min administration, high energy phosphate stores (HEP) are reduced at all Sr++ concentrations, but to the smallest extent at 10 mM Sr++, ISO at levels of 0.5 and 2 mM Sr++ induces a partial recovery of HEP, but at 5 and 10 mM a further reduction. Finally, under the influence of ISO the metabolic state is similar to that without ISO. Sr++ at high concentrations in absence of Ca++ seems to be capable of substituting in principle for Ca++ also concerning metabolism. Severe metabolic disturbances at low Sr++ concentrations indicate a failure of regulation of oxidative phosphorylation.