In vitro examination of cardiac tissues isolated from septic and endotoxin-shocked animals has demonstrated intrinsic decreased contractile function and has suggested calcium-related dysfunction. Both the sarcolemma (SL) and sarcoplasmic reticulum (SR) membranes have important roles in regulating cardiac free Ca2+ concentration. Therefore, calcium fluxes were examined in well-characterized SL and SR fractions isolated from hearts of control and endotoxin-shocked guinea pigs. Calcium pump activity was similar in SL from control and shock animals. No intrinsic alteration in the rate of equilibrium calcium concentration of Na(+)-Ca2+ exchange was observed in SL from shock guinea pigs. The electrogenic nature of the exchange was maintained. Active Ca2+ transport, Ca2(+)-ATPase activity, and Ca2+ efflux were similar in SR from hearts of control and shock animals. Although no intrinsic calcium dysfunction was noted in the sarcolemma or sarcoplasmic reticulum from the shock animals, this does not preclude the possibility that some factor (humoral agent) or condition (acidosis) may alter calcium processing in these membranes in vivo.
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