Calcium uptake by sarcoplasmic reticulum isolated from hearts of septic rats

Myocardial sarcoplasmic reticulum (SR) plays a critical role in the regulation of the cytosolic calcium fluctuations that occur during the cardiac cycle. One function of the SR is to lower the calcium concentration so that myocardial relaxation and thus ventricular filling can occur. The aim of the present study was to determine if hyperdynamic sepsis induced a decrease in the capacity of SR to take up calcium. This defect would result in decreased ventricular filling and thus decreased cardiac output, as has previously been shown in isolated perfused working hearts removed from septic rats. Therefore, rats were anesthetized with ether, and sepsis was induced by the injection of an aliquot of a fecal homogenate into the peritoneal cavity. Control animals either underwent surgery and received an aliquot of sterilized fecal inoculum (sham) or were untreated (no surgery). On day 2 after surgery, animals were anesthetized with pentobarbital, and hearts were removed, weighted, and SR isolated. The rate of uptake of 45Ca2+ by SR from septic rats was not depressed compared to controls but in fact was elevated. Maximum 45Ca2+ accumulated by the SR and Ca2+-stimulated ATPase activity were similar in SR from control and septic hearts. These results suggest that the contractile dysfunction noted in the myocardium in early sepsis is probably not due to inadequate SR removal of Ca2+ during diastole.