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

Departments of Pharmacology and Medicine, University of California, San Diego, La Jolla, California Submitted 4 June 2008 ; accepted in final form 3 January 2009 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 ET A receptor that couples to G q and G i proteins. Inhibition of G q -PLC-induced phosphoinositide (PI) hydrolysis with U73122 [GenBank] (1 µM) or inhibition of G i 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 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 G q and PTX-sensitive G i pathways. hypertrophy; sarcoplasmic reticulum calcium ATPase; G i ; G q Address for reprint requests and other correspondence: R. Hilal-Dandan, Univ. of California, San Diego, Dept. of Pharmacology, 9500 Gilman Dr., La Jolla, CA 92093-0636 (e-mail: rdandan{at}ucsd.edu )