RELEASE OF [ACETYLCHOLINE-H-3 FROM THE ISOLATED RETINA OF THE RAT BY POTASSIUM DEPOLARIZATION - DEPENDENCE ON HIGH AFFINITY CHOLINE UPTAKE

The effect of potassium depolarization on the release of [3H]‐acetylcholine ([3H]‐ACh) from the isolated retina of the rat was studied. Exposure of retinae to medium containing KC1 (50 mm) evoked a large increase in the efflux of [3H]‐ACh with only a small concurrent increase in the efflux of [3H]‐choline. The KCl‐evoked release of [3H]‐ACh was almost abolished in calcium‐free medium. Incubation of retinae with [3H]‐choline in sodium‐free medium, or medium containing hemi‐cholinium‐3 (HC‐3), procedures that are believed to inhibit selectively the high affinity choline transport system, reduced the retinal uptake of [3H]‐choline by approximately 50% and the synthesis of [3H]‐ACh by about 97%. The potassium‐evoked release of [3H]‐ACh was almost abolished in retinae that had been loaded with [3H]‐choline in sodium‐free medium or medium containing HC‐3, and subsequently superfused in normal medium. It is suggested that as in other areas of the nervous system, a sodium‐dependent, high affinity uptake system for choline is important in retinal cholinergic nerve terminals. 1979 British Pharmacological Society