Evoked release of tissue-bound exogenous [1--14C]acetylcholine from rat brain cortex slices.

Exogenous labeled acetylcholine ([14C]ACh) bound, in rat brain cortex slices, in a poorly (no non-)-exchangeable form, by prior incubation of the slices in presence of 5 mM [14C]ACh, is partly released in an ACh-free physiological saline-glucose-paraoxon medium by a variety of conditions. Among these are high [K+], lack of Na+ or Ca2+, and the presence of protoveratrine or ouabain. The releasing effect of protoveratrine is completely aboished by tetrodotoxin which itself is without effect. Only about half of the retained or tissue-bound [14C]ACh is affected by these conditions. The whole of the bound ACh is released by treatment with acid or by dissolution of the cell membranes. The stimuli that release part of the bound exogenous [14C]ACh appear to be similar to those that release glucose-derived tissue-bound ACh formed during normal cerebral metabolism.