PROPERTIES OF THE VIP-PACAP TYPE-II RECEPTOR STABLY EXPRESSED IN CHO CELLS

The VIP receptor cloned from rat lung (VIP, receptor from the group of the PACAP-VIP type II receptors) was inserted into a mammalian expres sion vector and stably transfected into Chinese hamster ovary cells (C HO). Two clones were selected, expressing respectively a high (850 +/- 50 fmol/mg protein, for clone 3) and a low (100 +/- 30 fmol/mg protei n for clone 16) number of receptors. Both crones had the same apparent K-d, value of binding for VIP and related peptides. The receptor expr essed had the same binding properties as the natural VIP receptor, jud ged from the relative potency of VIP and PACAP analogues and fragments . The EC(50) value of adenylate cyclase activation were 3 to 10 fold l ower in clone 3 than in 16. The values observed in clone 16 were close r to the binding K-d values. The differences between the two clones we re explained by the existence of spare receptors in clone 3, since: (a ) the relative efficacy of some fragments were lower in clone 16 than in clone 3; (b) pretreatment of the cells with VIP reduced the number of receptors in both clones and increased the EC(50) value for VIP in clone 3 but decreased peptide efficacy in clone 16 without significant change of the EC(50) value.