The effect of in vitro aging on human lung fibroblast beta-adrenergic receptor density, coupling and response.

Age-related changes in regulation of receptor response have been observed in several tissues and include regulation of beta-adrenergic receptor (beta-receptor) responses. The role of cellular aging in age-related changes in receptor response is not clear. We have examined the effect of aging in vitro on human fibroblast beta-receptor function. MRC-5 (embryonic lung) fibroblasts were aged by replication to produce cells of early, middle and late stages corresponding to the following cumulative population doublings: 15-20, 35-45 and greater than 50, respectively. Fibroblast membrane beta-receptor responses to isoproterenol (ISO, 0.1 mM) did not differ between the three stages. Adenylate cyclase responses to prostaglandin E1 (PGE1, 1 microM), guanosine triphosphate (GTP, 0.1 mM) and 5'-guanylimidodiphosphate (Gpp(NH)p, 0.1 mM) were also similar between the stages. Beta-receptor density (Bmax) was unaffected by in vitro aging. Beta-receptor agonist affinity, an indication of the capacity for beta-receptor coupling to the nucleotide binding protein (NS), was also unaffected by cell aging. These findings suggest that cellular aging in fibroblasts alone is not accompanied by changes in beta-receptor function.