Heart sarcolemmal Ca2+ transport in endotoxin shock: I. Impairment of ATP-dependent Ca2+ transport.

Effects of endotoxin administration on the ATP-dependent Ca2+ transport in canine cardiac sarcolemma were investigated. The results show that the sidedness of the sarcolemmal vesicles was not affected but the ATP-dependent Ca2+ transport in cardiac sarcolemma was decreased by 22 to 46% (p less than 0.05) at 4 h following endotoxin administration. The kinetic analysis indicates that the Vmax for ATP and for Ca2+ were decreased by 50% (p less than 0.01) and 32% (p less than 0.01), respectively, while the Km values for ATP and Ca2+ were not significantly affected after endotoxin administration. Magnesium (1-5 mM) stimulated while vanadate (0.25-3.0 microM) inhibited the ATP-dependent Ca2+ transport, but the Mg(2+)-stimulated and the vanadate-inhibitable activities remained significantly lower in the endotoxin-treated animals. These data demonstrate that endotoxin administration impairs the ATP-dependent Ca2+ transport in canine cardiac sarcolemma and that the impairment is associated with a mechanism not affecting the affinity towards ATP and Ca2+. Additional experiments show that the Ca2+ sensitivity of the Ca(2+)-ATPase activity was indifferent between the control and endotoxic groups suggesting that endotoxic injury impairs Ca2+ pumping without affecting Ca(2+)-ATPase activity. Since sarcolemmal ATP-dependent Ca2+ transport plays an important role in the regulation of cytosolic Ca2+ homeostasis, an impairment in the sarcolemmal ATP-dependent Ca2+ transport induced by endotoxin administration may have a pathophysiological significance in contributing to the development of myocardial dysfunction in endotoxin shock.