REGULATION AND BIOELECTRICAL EFFECTS OF CYCLIC ADENOSINE-MONOPHOSPHATE PRODUCTION IN THE CILIARY EPITHELIAL BILAYER

Purpose. To determine whether the intact isolated ciliary epithelial b ilayer retains the alpha-2 and beta adrenergic receptor activation and interaction described for whole ciliary processes and whether this pu re epithelial bilayer displays bioelectrical parameters sensitive to a lterations in cyclic adenosine Monophosphate (cAMP) production induced by adrenergic compounds. Methods. The intact ciliary epithelial bilay er of the rabbit eye isolated by perfusion was mounted in a specially constructed Ussing-type chamber, The transepithelial potential differe nce and short-circuit current were monitored for effects induced by ag ents that stimulated or blocked (some did both) cAMP production. Using a radioimmunoassay, the latter were studied in the pure epithelial bi layers and in whole ciliary processes, Results. A reproducible increas e in cAMP production and an increase in the short-circuit current indu ced in the bilayer by isoproterenol, a nonspecific beta adrenergic ago nist, were. both blocked by pretreatment with either timolol, a nonspe cific beta adrenergic blocking agent, or with para-aminoclonidine, an alpha-2 agonist. Maximal stimulation of cAMP with forskolin in this pu re isolated epithelial preparation yields a response that is 60% of th e value found in whole processes, indicating that the latter tissue co ntains responsive sites that are nonepithelial, probably vascular, or perhaps stromal. The degree of inhibition of the beta adrenergic recep tor by alpha-2 agonists was not very different in the two preparations . On the other hand, inhibition of the epithelial vasointestinal pepti de receptor by neuropeptide Yor alpha-2 agonism was considerably heigh tened in the pure bilayered epithelial preparation. Conclusions. The i solated intact ciliary epithelial bilayer, when stimulated with beta a drenergic receptor agonists, vasointestinal peptide, or forskolin, pro duces increased cAMP and its transepithelial potential becomes hyperpo larized. These chemical and bioelectrical effects are prevented by pre treatment with either alpha-2 adrenergic agonists or beta adrenergic b locking agents. The results obtained in the isolated intact purely epi thelial ciliary bilayer confirm that the ciliary epithelium is the sou rce of adrenergic receptor activation and interaction and support-the hypothesis that aqueous humor production is regulated by interactions between epithelial alpha-2 and beta adrenergic receptors.