Distinct mechanisms for the endocytosis of muscarinic receptors and G(q/11)

To determine whether the agonist-mediated endocytosis of muscarinic recepto rs and G(q/11) are mechanistically related events, the internalization of G (alpha q/11) was monitored under conditions established to prevent muscarin ic receptor endocytosis. Incubation of SH-SY5Y neuroblastoma cells with oxo tremorine-M resulted in the translocation of both muscarinic receptors and G(q/11) into a 'light vesicle' membrane fraction. Although muscarinic recep tor translocation was prevented by either the depletion of phosphoinositide s or by disruption of clathrin assembly, the endocytosis of G(q/11) was una ffected. These results demonstrate that the agonist-induced internalization of muscarinic receptors and G(q/11) proceed via distinct mechanisms. (C) 1 999 Elsevier Science B.V. All rights reserved.