VPAC(1) receptors have different agonist efficacy profiles on membrane and intact cells.
The vasoactive intestinal peptide receptor VPAC(1) is preferentially coupled to G(alpha s) protein but also increases [Ca(2+)](i) through interaction with G(alpha i)/G(alpha q) protein. We evaluated a panel of full, partial and null agonists for their capability to stimulate adenylate cyclase activity in both intact cells and membrane and [Ca(2+)](i) in intact cells transfected with the reporter gene aequorin. In intact cells, the agonists efficacy for cAMP and calcium increase were well, but not linearly correlated: VPAC(1) receptors activated G(alpha s) protein more efficiently but with the same pharmacological profile as the other G proteins. In contrast, there was a difference between cAMP increase in intact and broken cell membranes: EC(50) values were generally lower in intact cells whereas the efficacy was higher. There was, however, no correlation between the shift in the EC(50) value and the intrinsic activity. Of interest, the (4-28) fragment, a reported antagonist on cell membrane, was a full agonist in intact cells. We concluded that the active states of the VPAC(1) receptor resulting from the coupling to different effector are undistinguishable by the VIP analogs tested but that receptor properties are different when evaluated in intact cells or cell membranes.
Langer
Ingrid
I
Department of Biological Chemistry and Nutrition, Faculty of Medicine, Université Libre de Bruxelles, Bat GE, CP 611, 808 Route de Lennik, B-1070 Brussels, Belgium. ilanger@ulb.ac.be
Vertongen
Pascale
P
Perret
Jason
J
Cnudde
Johnny
J
Gregoire
Françoise
F
De Neef
Philippe
P
Robberecht
Patrick
P
Waelbroeck
Magali
M
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D018005:Receptors, Vasoactive Intestinal Peptide / Q000819:agonists*; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D018005:Receptors, Vasoactive Intestinal Peptide; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; D014660:Vasoactive Intestinal Peptide; D000262:Adenylyl Cyclases; D002118:Calcium