Down regulation 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 ET_A receptor that couples to G_q and G_i proteins. Inhibition of G_q-PLC induced phosphoinositide (PI) hydrolysis with U7-3122(1µM) or inhibition of Gi protein with pertussis toxin (PTX) abolishes the ability of ET to downregulate SERCA2 mRNA gene expression. Further investigation suggests that ET coupling to PTX-sensitive G_i with consequent lowering of cAMP is required for down regulation of SERCA2 mRNA levels. Increasing intracellular cAMP quantity using cAMP specific PDE inhibitor Ro20-1724 or cAMP analog db-cAMP reverses ET induced down regulation 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 G_q and PTX-sensitive G_i pathways.