770-5 Chamber Specific Regulation of the Sarcoplasmic Reticulum Calcium ATPase Pump In Human Heart Failure

Abstract

Alterations in the expression of Ca 2+ channels have been described in failing human left ventricle, including down regulation of the ryanodine receptor (RyR)/Ca 2+ release channel and the sarcoplasmic reticulum Ca 2+ ATPase pump (SERCA) which are involved in excitation-contraction coupling and relaxation (Cir Res 71: 18, 1992). We previously reported chamber specific regulation of the RyR during end-stage human heart failure (Clin Res 42(2):166A. 1994). We investigated whether SERCA is also regulated in the other cardiac chambers during human heart failure. Total RNA and protein homogenates were isolated from the left and right atria (LA, RA) and left and right ventricles (LV, RV) obtained prospectively from 32 cardiac transplant patients and 4 normal controls. Messenger RNA (mRNA) levels of SERCA were quantified using Northern and slot blot hybridizations with a 1.6 kb rat cardiac SERCA cDNA probe and normalized to 28S ribosomal levels. Protein levels of SERCA were quantified using enzyme-linked immunosorbent assays with monoclonal antibodies directed against dog cardiac SERCA. Northern analyses detected a single ≈4 kb mRNA in all regions. Compared to controls. SERCA mRNA expression in failing hearts was decreased in LV by 39% (p < 0.005), unchanged in RV, and increased in LA by 255% (p < 0.005) and in RA by 338% (p < 0.025). Consistent with the mRNA data. immunodetectable levels of SERCA were also reduced in LV by 30% (p < 0.05) and unchanged in RV; however, protein levels appeared unchanged or reduced in both atria in contrast to the mRNA. This is the first study reporting simultaneous measurements of SERCA mRNA and protein levels in the human heart. We conclude that chamber specific regulation of SERCA mRNA occurs during end-stage heart failure. corroborated by protein expression in the ventricles. Down regulations of SERCA may contribute to impaired relaxation and increased diastolic tone during heart failure.