Subunit expression of signal transducing G proteins in cardiac tissue: implications for phospholipase C-beta regulation.

In the heart, alpha-adrenergic, angiotensin II and endothelin signaling pathways modulate short-term changes in chronotropy and inotropy, and participate in the long-term control of cardiac growth. A shared feature of these signaling pathways is the stimulation of phosphatidylinositol (PI) turnover, which is thought to occur via G protein-mediated regulation of phospholipase C (PLC) activity. However, G protein subunits capable of regulating PLC activity have not been identified in different regions and cell types of the heart and members of the G protein-regulated PLC-beta isozyme family have not been documented in the heart. Using a battery of antipeptide specific antisera directed against the G protein alpha q, beta and gamma subunit families and against members of the PLC-beta, PLC-gamma and PLC-delta families, we demonstrated that heart tissues express the G protein alpha subunits alpha q and alpha 11, multiple G protein beta and gamma subunits, and PLC-beta 3, a phospholipase C isozyme regulated by either G protein alpha or beta gamma subunits. The degree of expression and distribution of these subunits differed between regions of the heart (atria versus ventricle) and changed with development. These data lay the ground work for future studies to determine the functional coupling of specific subsets of these components involved in receptor activation of PI turnover in the heart.