G protein modulation of voltage-sensitive muscarinic receptor signalling in mouse pancreatic acinar cells

Submaximal stimulation of mouse pancreatic acinar cells by acetylcholine (A Ch) generates periodic Ca2+ responses sensitive to the membrane potential. Monitoring the muscarinic Ca2+ responses using patch-clamp whole-cell curre nt recordings, we examined the mechanism of guanine nucleotide-binding prot ein (G protein)-receptor interaction in terms of the membrane potential. Th e lowest ACh concentration able to elicit consistent repetitive spikes was 50 nM, in the presence of which hyperpolarization increased and depolarizat ion decreased the spike frequency. The saturating concentration was 10 CIM, this induced a sustained response insensitive to voltage. Internal guanosi ne 5'-tri- and diphosphates (GTP, GDP) depressed and potentiated the voltag e sensitivity, respectively, but not for the response to a saturating ACh c oncentration (10 CIM). Internal guanosine 5'-O-(3-thiotriphosphate) (GTP ga mmaS) abolished the voltage sensitivity. The results indicate that the ACh- induced Ca2+ response is sensitive to the membrane potential and that a clo se linkage exists between voltage sensitivity and the G protein association /dissociation cycle in the muscarinic receptor.