SERCA Cys674 sulphonylation and inhibition of L-type Ca2+ influx contribute to cardiac dysfunction in endotoxemic mice, independent of cGMP synthesis

Abstract

The goal of this study was to identify the cellular mechanisms responsible for cardiac dysfunction in endotoxemic mice. We aimed to differentiate the roles of cGMP [produced by soluble guanylyl cyclase (sGC)] versus oxidative posttranslational modifications of Ca2+ transporters. C57BL/6 mice [wild-type (WT) mice] were administered lipopolysaccharide (LPS; 25 μg/g ip) and euthanized 12 h later. Cardiomyocyte sarcomere shortening and Ca2+ transients (ΔCai) were depressed in LPS-challenged mice versus baseline. The time constant of Ca2+ decay (τCa) was prolonged, and sarcoplasmic reticulum Ca2+ load (CaSR) was depressed in LPS-challenged mice (vs. baseline), indicating decreased activity of sarco(endo)plasmic Ca2+-ATPase (SERCA). L-type Ca2+ channel current ( ICa,L) was also decreased after LPS challenge, whereas Na+/Ca2+ exchange activity, ryanodine receptors leak flux, or myofilament sensitivity for Ca2+ were unchanged. All Ca2+-handling abnormalities induced by LPS (the decrease in sarcomere shortening, ΔCai, CaSR, ICa,L, and τCa prolongation) were more pronounced in mice deficient in the sGC main isoform (sGCα1−/− mice) versus WT mice. LPS did not alter the protein expression of SERCA and phospholamban in either genotype. After LPS, phospholamban phosphorylation at Ser16 and Thr17 was unchanged in WT mice and was increased in sGCα1−/− mice. LPS caused sulphonylation of SERCA Cys674 (as measured immunohistochemically and supported by iodoacetamide labeling), which was greater in sGCα1−/− versus WT mice. Taken together, these results suggest that cardiac Ca2+ dysregulation in endotoxemic mice is mediated by a decrease in L-type Ca2+ channel function and oxidative posttranslational modifications of SERCA Cys674, with the latter (at least) being opposed by sGC-released cGMP.