Abstract
We have characterized vasoactive intestinal peptide (VIP) receptor/G-protein coupling in rat alveolar macrophage (AM) membranes and find that pertussis toxin treatment and antisera against Gαi3 and Gαs reduce high-affinity 125I-VIP binding, indicating that both Gαs and Gαi3 couple to the VIP-receptor. The predominant VIP-receptor subtype in AM is VPAC1 and we examined the G-protein interactions of the human VPAC1 that had been transfected into HEK293 cells. VPAC1 has a molecular mass of 56 kDa; GTP analogs reduced 125I-VIP binding to this protein demonstrating that high-affinity binding of VIP to the receptor requires coupling to G-protein. Functional VIP/VPAC1/G-protein complexes were captured by covalent cross-linking and analyzed by Western blotting. The transfected human VPAC1 receptor in HEK293 was found to be coupled to Gαs but not Gαi or Gαq. Furthermore, pertussis toxin treatment had no effect on VPAC1/G-protein coupling in these cells. These observations suggest that the G-proteins activated by VPAC1 may be dependent upon species and cell type.
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