Alpha 1-adrenergic and m3-muscarinic receptor stimulation of phosphatidylinositol 4,5-bisphosphate-specific phospholipase C are independently mediated by G alpha q/11 in rat parotid gland membranes.

Stimulation of m3-muscarinic cholinergic receptors (m3AChR) in the rat parotid gland increases the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) via activation of the G alpha/11 family of G-proteins (Sawaki et al. (1993) Arch. Biochem. Biophys., 546-550). Herein we report that alpha 1-adrenergic receptor (alpha 1-AR) stimulation of PIP2 hydrolysis is also mediated via alpha subunits of the G q/11 family of G-proteins. The alpha 1-AR agonist, epinephrine, induced a dose-dependent increase (1.5-fold maximum) of exogenously added PIP2 in the presence of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), which was inhibited by the alpha 1-AR antagonist, phentolamine, but not by the beta-adrenergic receptor antagonist, propranolol. The epinephrine-stimulated component of PIP2 hydrolysis was significantly inhibited by pretreating the membranes with an antiserum against G alpha q/11. When carbachol and epinephrine were present simultaneously (with GTP gamma S), the increase in PIP2 hydrolysis obtained was not significantly different from the sum of the increases in PIP2 hydrolysis obtained with each agonist alone. PIP2 hydrolysis stimulated in the presence of carbachol and epinephrine was inhibited by alpha 1-AR and m3AChR antagonists, phentolamine and atropine respectively, to the level obtained with each agonist alone. Notably, in the presence of both agonists the inhibition of PIP2 hydrolysis by anti-G alpha q/11 antiserum was not significantly different from the sum of the inhibitions obtained with each agonist alone. These results indicate that m3AChR and alpha 1-AR stimulation of PIP2 hydrolysis in rat parotid gland membranes are independently mediated by the G alpha q/11 family of G-proteins.