Developmental changes in α₁-adrenoceptor coupling to G-protein in bovine aorta

Differences in epinephrine binding to α1-adrenoceptors, epineprhine-induced contractile potency, susceptibility to phorbol ester (PDBu) modulation, and differences in membrane fluidity were studied in bovine aorta from young (3-8 weeks) and adult or mature (6-8 years) animals. Membranes prepared from aorta of adult animals exhibited a two-fold higher receptor density while [3H]prazosin affinity was unchanged. Epinephrine displacement studies revealed both high- and low-affinity binding in membranes from the aortas of young animals whereas, preparations from adult animals exhibited only a single class of low-affinity sites. In low-temperature binding studies, membranes prepared from aortas of adult animals exhibited both high- and low-affinity agonist binding, in proportions about equal to those of young animals. The ability of PDBu to uncouple α1-adrenoceptor from G-protein interaction is demonstrable in young but not in adult animals which raises the possibility of prior phosphorylation of receptors in the latter tissues. Aortas from young animals showed increased contractile potency to epinephrine and, in addition, were significantly more fluid as compared to aortas from adult animals. Alterations in the membrane environment or phosphorylation state of the α1-adrenoceptor may thus provode age-dependent modulation of its function.