SPECIFICITY OF G(Q) AND G(11) PROTEIN SIGNALING IN VASCULAR MYOCYTES

The molecular diversity of receptors and the capability of these recep tors to activate multiple types of G proteins theoretically allow the transmission of signals through multiple effector pathways. In functio nal experiments, however, the number of possibilities may be strongly reduced. We have recently reported that in vascular myocytes, alpha(1) -adrenoceptors activate two G proteins composed of alpha(1)/beta(1)/ga mma(3) and alpha(11)/beta(3)/gamma(2) subunits, leading to increase in cytoplasmic [Ca2+](i) concentration. Only the alpha(q) subunit transd uces the signal to phospholipase C-beta, which hydrolyzes phosphatidyl inositol 4,5-bisphosphate to generate inositol 1,4,5-trisphosphate and the subsequent release of Ca2+ from the intracellular store. In contr as, the alpha(11) subunit activates Ca2+ entry through a nonspecific c ation channel in the presence of increased [Ca2+](i) level. These coup ling mechanisms reveal the distinct participation of G(q) and G(11) in the regulation of vascular contractility. Specific G(q)- or G(11)-act ivated pathways should be taken into account to understand the various contraction profiles induced by different vasoconstrictors. (C) 1998, Elsevier Inc.