Relationship between agonist binding, phosphorylation and immunoprecipitation of the m3-muscarinic receptor, and second messenger responses

Open Access
Publisher Website
Google Scholar
Abstract
1 Phosphoinositidase C-linked m3-muscarinic receptors expressed in Chinese hamster ovary cells (CHO-m3 cells) are phosphorylated on serine following agonist stimulation 2 m3-Muscarinic receptor phosphorylation is concentration-dependent requiring a carbachol concentration of 13.2 μm for half maximal stimulation 3 The phosphorylation concentration-response curve lies to the left of the curve for carbachol binding to muscarinic receptors (KD=100μm) in membranes from CHO-m3 cells. In contrast, receptor phosphorylation closely correlates with receptor-mediated phosphoinositidase C activation (EC50 for inositol 1,4,5 trisphosphate accumulation during the peak and plateau phases were 7.14 μm and 5.92 μm respectively) but not with rapid agonist-mediated calcium elevation (EC50 = 0.32 μm) measured in fura-2-AM loaded cells 4 These data suggest a dissociation of receptor phosphorylation from agonist occupation. Such an apparent ‘receptor reserve’ for m3-muscarinic receptor phosphorylation may be indicative of a mechanism that is dependent on a small amplification of the receptor signal, though probably dissociated from the calcium signal.

This publication has 22 references indexed in Scilit: