Specificity of G(q) and G(11) Protein Signaling in Vascular Myocytes

Abstract

The molecular diversity of receptors and the capability of these receptors to activate multiple types of G proteins theoretically allow the transmission of signals through multiple effector pathways. In functional experiments, however, the number of possibilities may be strongly reduced. We have recently reported that in vascular myocytes, α(1)-adrenoceptors activate two G proteins composed of α(q)/β(1)/γ(3) and α(11)/β(3)/γ(2) subunits, leading to increase in cytoplasmic [Ca(2+)](i) concentration. Only the α(q) subunit transduces the signal to a phospholipase C-β, which hydrolyzes phosphatidylinositol 4,5-bisphosphate to generate inositol 1,4,5-trisphosphate and the subsequent release of Ca(2+) from the intracellular store. In contrast, the α(11) subunit activates Ca(2+) entry through a nonspecific cation channel in the presence of increased [Ca(2+)](i) level. These coupling mechanisms reveal the distinct participation of G(q) and G(11) in the regulation of vascular contractility. Specific G(q)- or G(11)-activated pathways should be taken into account to understand the various contraction profiles induced by different vasoconstrictors.