Regional distribution of acetylcholine and associated enzymes and their regeneration in corneal epithelium.

Acetylcholine and choline acetyltransferase are found in high concentrations in the corneal epithelium of most species, although their function is unknown. We have measured the levels of each in different regions of the rabbit cornea and found that both are much more abundant in central than in peripheral cornea or conjunctival epithelium. Following abrasion of the cornea, epithelial cells from the surrounding cornea or conjunctiva move over rapidly and regenerate. We have assayed choline acetyltransferase and total protein after complete or incomplete abrasion of the corneal epithelium. Acetylcholine-synthesizing activity was not detectable in the regenerating cells until 14-21 days later (depending on the degree of abrasion). Like glycogen and oxidative enzymes, which are also much more abundant in corneal than conjunctival epithelium, choline acetyltransferase regeneration is complete about 28 days after abrasion. In contrast with acetylcholine and choline acetyltransferase, cholinesterase activity is low and its distribution relatively uniform over cornea and conjunctiva. The high ratio of acetylcholine synthesis to cholinesterase activity suggests that acetylcholine released from the corneal epithelium would be able to diffuse to more distant structures within the eye.