Endothelin downregulates SERCA2 gene and protein expression in adult rat ventricular myocytes: regulation by pertussis toxin-sensitive Giprotein and cAMP

Abstract

Downregulation of the sarcoplasmic reticulum calcium ATPase (SERCA2) is associated with diastolic dysfunction in the failing heart. Elevated plasma endothelin-1 (ET) levels are correlated with congestive heart failure suggesting that ET may play a pathophysiological role. We have investigated the ability of ET to regulate SERCA2 gene expression in isolated adult rat ventricular myocytes. We find that ET enhances net protein synthesis by ∼40% but significantly downregulates SERCA2 mRNA expression, time dependently, by ∼30–50%, and the expression of SERCA2 protein by ∼ 50%. In myoyctes, ET binds to ETAreceptor that couples to Gqand Giproteins. Inhibition of Gq-PLC-induced phosphoinositide (PI) hydrolysis with U73122 (1 μM) or inhibition of Giprotein with pertussis toxin (PTX) abolishes the ability of ET to downregulate SERCA2 mRNA gene expression. Further investigation suggests that ET coupling to PTX-sensitive Giwith consequent lowering of cAMP is required for downregulation of SERCA2 mRNA levels. Increasing intracellular cAMP quantity using cAMP-specific PDE inhibitor Ro20-1724 or cAMP analog dibutyryl-cAMP reverses ET-induced downregulation of SERCA2 mRNA levels. The data indicate that, in adult myocytes, ET downregulates SERCA2 mRNA and protein levels, and the effect requires cross-talk between Gqand PTX-sensitive Gipathways.