Differential effect of arachidonic acid on the vasoactive intestinal peptide receptor/effector system in rat prostatic epithelium during sexual maturation

The effects of alterations in the membrane lipid environment on vasoactive intestinal peptide (VIP) binding and VIP-stimulated cyclic AMP accumulation have been analyzed by arachidonic acid treatment of prostatic epithelial cells from rats at puberty and maturity, two critical developmental periods with characteristic lipidic and androgenic statuses. Treating cells with 0.1 mM arachidonic acid for 15 min at 37°C increased the affinity of VIP receptors and the potency of the neuropeptide (up to five times) in the formation of cyclic AMP at maturity, but not at puberty. The average plasma membrane fluidity (as measured by fluorescence polarization of diphenylhexatriene) remained unmodified after arachidonic acid treatment of cells. The modifications observed in mature rats were specific for the VIP receptor/effector system, since cyclic AMP stimulation by isoproterenol or forskolin was not affected by cell treatment with arachidonic acid. These results are compatible with the existence of a particular lipidic microdomain surrounding the VIP receptor in the cell membrane that would be altered by exposure to arachidonic acid (either directly or through conversion of arachidonic acid to its metabolites, as suggested by experiments on inhibition of the arachidonic acid cascade). This would make it possible for the activation of protein kinase C to phosphorylate VIP receptors in cells from mature rats, but not in those from pubertal animals with a very different membrane lipid composition (as suggested by the corresponding values of membrane fluidity and transition temperature).