Alternation of Na(+)-Ca2+ exchange in rat cardiac sarcolemmal membranes during different phases of sepsis

To study the alteration of Na(+)-Ca2+ exchange in rat cardiac sarcolemmal membrane during phases of septic shock. Sepsis was induced by cecal ligation and puncture (CLP). Na(+)-Ca2+ exchange was assayed by radioactive analysis. Na(+)-dependent 45Ca2+ uptake was decreased by 62%-69% in late phase of sepsis, whereas it was not affected in early phase of sepsis. Na(+)-Ca2+ exchange stimulated by 5' guanylyl imidodiphosphate [Gpp (NH) p] was decreased by 65.7% in late phase of sepsis but unaltered in early phase of sepsis. Two agonists (angiotensin II and phenylephrine) coupled to Gq and a protein kinase C activator, phorbol 12-myristate 13-acetate (PMA) all inhibited Na(+)-Ca2+ exchange in late phase of sepsis. Na(+)-Ca2+ exchange activities induced by phosphorylation of Na(+)-Ca2+ exchange were decreased in late phase of sepsis, whereas inhibition of Na(+)-Ca2+ exchange by dephosphorylation was increased both in early and late phases of sepsis. The alteration of Na(+)-Ca2+ exchange during different phases of sepsis might be related to the activities of Gq, protein kinase C, and phosphorylation/dephosphorylation.