THE G-ALPHA PROTEIN G(L2)ALPHA IMPROVES THE ABILITY TO DETECT THE SUBTHRESHOLD EXPRESSIONS OF RECEPTORS LINKED TO PHOSPHOLIPASE-C IN XENOPUS OOCYTES

Xenopus laevis oocytes showed no electrophysiological responses to ace tylcholine (ACh) and had no significant cholinergic receptor sites whe n prepared under our conditions. However, they were found to acquire r obust electrophysiological responsiveness to ACh when bovine G(L2)alph a, which is a member of the G(q) alpha family and is highly homologous to mouse G(11)alpha, was expressed by mRNA injection. Further analyse s indicated that G(L2)alpha amplified the activity of endogenous musca rinic ACh receptors that are expressed at an otherwise undetectable le vel, and thus made their detection possible. Thus, G(L2)alpha may prov e to be an effective method for detecting the activities of phospholip ase C-linked receptors which are only marginally expressed. The useful ness of this method was confirmed in the analyses of a chimeric recept or constructed from metabotropic glutamate receptor subtype la and mus carinic ACh receptor subtype M1. The chimeric receptor showed no elect rophysiological responses to ACh when expressed alone in oocytes, but became responsive to ACh when cc-expressed with G(12)alpha.