ISOLATION OF NEONATAL CARDIOMYOCYTES REDUCES THE EXPRESSION OF THE GTP-BINDING PROTEIN, G(H)

alpha(1)-Adrenoceptors in most tissues couple with the heterotrimeric GTP-binding protein G(q), the alpha subunit of which activates the bet a-isoforms of phospholipase C. However, in heart (and in liver) alpha( 1)-adrenoceptors have been reported to couple to a high molecular weig ht GTP-binding protein, G(h), which functions both as a type II transg lutaminase and as a receptor coupling protein. G(h) activates a phosph olipase isoform distinct from phospholipase C-beta. Here we report tha t isolation and culture of neonatal cardiomyocytes decreased the expre ssion of G(h) without reducing the content of G(q) or G(l), G(h) was r eadily detected in extracts from intact neonatal and adult heart tissu es. The expression of G(h) thus appears to be a feature of intact card iac tissue. (C) 1995 Academic Press Limited