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Abstract
Serotonin increases the level of cyclic AMP in incubated rabbit corneas; the concentration of agonist producing half-maximal stimulation is approximately 1.5 microM. Nialamide, an inhibitor of monoamine oxidase, potentiates the response to serotonin but not to epinephrine. Amitriptyline, an inhibitor of neuronal uptake of serotonin, does not potentiate the stimulation of cyclic AMP synthesis. Lysergic acid diethylamide, but not timolol, antagonizes the response to serotonin; the half-maximal inhibitory concentration is approximately 6 nM lysergic acid diethylamide. A comparison of the time course of the increase in cyclic AMP synthesis after addition of serotonin or epinephrine to the incubation media indicates that serotonin, but not epinephrine, must penetrate a barrier to its free diffusion. We conclude that the corneal epithelium contains specific serotonergic receptors that, upon activation, cause the synthesis of cyclic AMP, which mediates the stimulation of chloride transport (c.f. companion article, Klyce et al.). The serotonergic receptors must be at a location posterior to the beta-adrenergic receptors, which are on the anterior-surface of the apical cells.