Alteration of corneal epithelial ion transport by sympathectomy

The cornea is dually innervated, receiving afferent nerves from the trigeminal ganglion and efferent nerves from the superior cervical ganglion. This study examines the specific effects of superior cervical ganglionectomy (SCGX) on the in vitro ion transport characteristics of the rabbit corneal epithelium. Two weeks after SCGX, epithelial Cl^--dependent transport and total ionic conductance were increased in comparison to values obtained in paired control eyes. This increased transport level appeared to be independent of membrane receptor activity as demonstrated by lack of responsiveness to α-adrenergic, β-adrenergic, serotonergic, dopaminergic, nicotinic cholinergic, or muscarinic cholinergic blockade. Nevertheless, SCGX produced a supersensitivity to epinephrine-stimulated transport as measured by the responsiveness of the ion transport current. Furthermore, SCGX abolished the responsiveness of the epithelium to serotonin. On the basis of these and earlier findings, the authors conclude that corneal sympathetic innervation influences membrane and receptor properties. Autonomic neurotrophic effects in the corneal epithelium include suppression of apical membrane Cl^- permeability and of β-adrenoreceptor sensitivity to biogenic amines. It is proposed that the corneal serotonergic receptors that activate Cl^- transport lie on the sympathetic nerve terminals and stimulate this transport process by causing the neural release of a catecholamine.