Abstract
Carbachol stimulation of phosphatidylinositol 4,5-bisphosphate (PIP 2) hydrolysis by rat parotid gland membranes is dependent on the presence of GTPγS and is a result of m 3-muscarinic receptor regulation of G-protein coupled, PIP 2-specific phospholipase C (PLC). The PLC activity (>80%) was solubilized with 1% Na-cholate but the solubilized enzyme was not stimulated by GTPγS and carbachol. Immunoblotting of rat parotid membranes with polyclonal antiserum, which recognizes α-subunits of the G q/11 family, indicated the presence of two immunoreactive proteins of approximate molecular weights 41 and 42 kDa. Incubation of membranes with the common G αq/11 antiserum attenuated the stimulation of PIP 2 hydrolysis, induced by GTPγS alone and by carbachol, in the presence of GTPγS. The antiserum had no effect on PIP 2 hydrolysis in unstimulated membranes or in the cholate extract, where it is uncoupled from the G-protein. Antiserum against G αi, which is also coupled to the m 3-muscarinic receptor in this tissue, had no effect on either basal or stimulated PIP 2 hydrolysis. These results demonstrate that in rat parotid gland, activation of PIP 2-specific PLC by m 3-muscarinic receptor stimulation is mediated via α-subunits of the G q/11 family of G-proteins.
Published Version
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