Pharmacological properties of Chinese hamster ovary cells coexpressing two vasoactive intestinal peptide receptors (hVPAC1 and hVPAC2).

1. In the light of recent findings that VPAC1 and VPAC2 receptors form homodimers and heterodimers, we have evaluated the function of these receptors coexpressed in the same cells, using whole-cell and membrane preparations. Cells expressing each receptor alone were used for comparison. 2. The study was performed on Chinese hamster ovary cells stably transfected with both human recombinant receptors and we compared receptor occupancy and adenylate cyclase activation by VIP, Ro 25-1553 - a VPAC2 selective agonist - and [K(15),R(16),L(27)]VIP(1-7)/GRF(8-27) - a VPAC1 selective agonist - on membranes prepared from each cell line and on a mixture of membranes from cells expressing each receptor individually. We also studied receptor internalization induced by the three agonists on intact cells expressing both receptors alone or together by fluorescence-activated cell sorting using monoclonal antibodies and demonstrated by using co-immunoprecipitation that the two receptors did interact.3. The results indicated that coexpression of the receptors did not modify the recognition of ligands, nor the capacity of the agonists to stimulate adenylate cyclase activity and, in intact cells, to induce internalization of the receptors.4. As a consequence, the properties of the selective ligands that were established on cell lines expressing a single population of VIP receptors were valid on cells expressing both receptors. Furthermore, the recently demonstrated VPAC1/VPAC2 receptor heterodimerization did not affect the function of either receptor.