Induction of functional β-adrenergic receptors in rat aortic smooth muscle cells by sodium butyrate

Abstract

Rat aortic smooth muscle cells in culture (A-10; ATCC CRL 1476) exhibited low levels of β-adrenergic receptors as determined by specific binding of [125I]cyanopindolol ([125I]CYP) and marginal stimulation of adenylate cyclase in plasma membranes by (−)isoproterenol. When these cells were exposed to 5 mM sodium butyrate, the number of β-adrenergic receptors and the β-agonist-stimulated adenylate cyclase activity increased markedly. However, basal, GTP, Gpp(NH)p, and fluoride-stimulated activities did not change. The induction of β-adrenergic receptors and β-agonist stimulated adenylate cyclase activity was time- and dose-dependent, and was relatively specific for sodium butyrate. Propionate and valerate were less effective than butyrate, while isobutyrate, succinate, and malonate were ineffective. The induction involved RNA and protein synthesis because induction was prevented by treatment with cycloheximide, puromycin, and actinomycin D. Butyrate did not cause a general increase in cell surface receptors, because the number of vasopressin receptors did not change. The sustained presence of butyrate appeared to be necessary for the maintenance of the induced β-receptors. When butyrate was removed, receptor number and β-agonist-stimulated adenylate cyclase activity were decreased by 90% over 24 hr. We conclude that the poor response of rat aortic smooth muscle cell plasma membranes to β-adrenergic agonists is due to the presence of a low number of β-adrenergic receptors. Butyrate markedly increased the number of β-receptors which resulted in a proportional increase in β-agonist-stimulated adenylate cyclase activity. The increase in receptor number was dependent on RNA and protein synthesis. Butyrate treatment did not affect the activity of the cyclase unit and the efficiency of coupling between the receptors and the guanine nucleotide regulatory protein, Ns.