CALCIUM AND CALMODULIN REGULATE LIPOPOLYSACCHARIDE-INDUCED ALVEOLAR MACROPHAGE PRODUCTION OF TUMOR-NECROSIS-FACTOR AND PROCOAGULANT ACTIVITY

Background: Alterations in macrophage (M phi) function are responsible , in part, for adult respiratory distress syndrome and multiple organ failure developing in patients with sepsis. Elucidation and control of these M phi mechanisms during sepsis are crucial to our understanding of this disease and, ultimately, to improving survival of these patie nts. Objective: To investigate the involvement of calcium flux in endo toxin-induced alveolar M phi production of tumor necrosis factor (TNF) and procoagulant (PC) activity. Design: Rabbit alveolar M phi obtaine d by bronchoalveolar lavage were exposed to endotoxin in the form of l ipopolysaccharide (LPS) extracted from Escherichia coli 0111:B4 in the presence of different specific calcium agonists and antagonists. The TNF expression was measured in the supernatant by L929 bioassays. The PC activity was determined in cell lysates by a one-step coagulation a ssay. Results: Macrophages activated by LPS produce enormous levels of TNF and PC. Either W7 (20 mu mol/L), a calmodulin antagonist, or TMB- 8 (50 mu mol/L), which prevents calcium release from the endoplasmic r eticulum, inhibited production of both TNF and PC activity. Verapamil (50 mu mol/L) alone or combined with TMB-8 significantly inhibited bot h TNF and PC production by LPS-stimulated M phi. Elevating intracellul ar calcium ([Ca2+]i), using the calcium ionophore, A23187, or thapsiga rgin alone, did not induce M phi production of TNF but significantly a ugmented LPS-stimulated TNF production. Conclusion: Our results indica te that increased intracellular calcium causing signal transduction ac tivation through the calmodulin pathway is a necessary, but insufficie nt, component of the LPS signaling in M phi.