EFFECTS OF SURGICAL SYMPATHETIC DENERVATION ON G-PROTEIN LEVELS, ALPHA-ADRENERGIC AND BETA-ADRENERGIC RECEPTORS, CAMP PRODUCTION AND ADENYLATE-CYCLASE ACTIVITY IN THE SMOOTH MUSCLES OF RABBIT IRIS

The relative densities of a number of G protein subunits were quantifi ed in membranes prepared from iris sphincter and dilator muscles of ra bbits that have undergone sympathetic denervation and from contralater al innervated controls by immunoblotting with specific polyclonal anti bodies against Gs alpha, Gi alpha and Gq alpha protein subunits. In ad dition, alpha and beta-adrenergic receptor densities, basal and isopro terenol (ISO)-stimulated cAMP production, and basal and ISO + GTP gamm a S-stimulated adenylate cyclase (AC) activities were measured in the same tissues. Densitometric analysis of the immunoblot data revealed a 32% reduction in the level of Gi alpha in the denervated sphincter, a 26% increase in the level of Gi alpha in the denervated dilator, and no changes due to denervation were found in the levels of Gs alpha and Gq alpha. Sympathetic denervation had no effect on the densities of a lpha-and beta-adrenergic receptors in these tissues, however, it did i nduce a significant decrease in the K-D values of a-adrenergic recepto rs in both dilator and sphincter, and in beta-adrenergic receptors in the sphincter. The basal- and ISO-stimulated cAMP production in the sp hincter was 4-fold as high as that of the dilator, and at 0.05 mu M IS O the denervation supersensitivity for cAMP production in the sphincte r increased by 118% as compared to 36% in the dilator. Sympathetic den ervation increased by 19-47% the basal- and ISO-stimulated activity of AC in these tissues, however, it had no effect on the phospholipase C activity. We conclude that changes in Gi alpha levels, adrenergic rec eptor affinity, cAMP accumulation and AC activity are involved in the mechanism of sympathetic denervation supersensitivity and subsensitivi ty of the iris of the eye. In addition, these findings add further sup port to the developing hypothesis that the sympathetic nervous system can regulate, through alterations in cAMP levels, muscarinic responses (parasympathetic) in the smooth muscles of the iris-ciliary body.