Cell Cycle-dependent Coupling of the Vasopressin V1a Receptor to Different G Proteins

Arginine vasopressin (AVP) regulates biological processes by binding to G protein-coupled receptors. In Swiss 3T3 fibroblasts, expressing the V1a subtype of vasopressin receptors, AVP mobilizes calcium from intracellular stores. In proliferating cells, the AVP-induced increase in intracellular calcium concentration ([Ca2+]i) was mediated by G proteins of the Gq family, which are insensitive to pertussis toxin (PTX) pretreatment of the cells. In quiescent cells, the AVP-induced increase in [Ca2+]i was partially PTX-sensitive, suggesting an involvement of Gi proteins. We confirmed this by photoaffinity labeling of G proteins in Swiss 3T3 cell membranes activated by AVP. In Swiss 3T3 cells arrested in the G0/G1 phase of the cell cycle, the AVP-induced increase in [Ca2+]i was also partially PTX-sensitive but was PTX-insensitive in cells arrested in other phases of the cell cycles. The blocking effect of PTX pretreatment in G0/G1 cells was mimicked by microinjection of antisense oligonucleotides suppressing the expression of the Gαi3 subunits. These results were confirmed by microinjection of antibodies directed against the C terminus of G protein α-subunits. The data presented indicate that in Swiss 3T3 fibroblasts synchronized in the G0/G1 phase of the cell cycle the V1a receptor couples to Gq/11 and Gi3 to activate the phospholipase C-β, leading to release of intracellular calcium.