Vesicular Storage and Release of Cholinergic False Transmitters

Abstract

Several analogues of choline are known, which are taken up by cholinergic nerve terminals and released in the acetylated form on stimulation. Such compounds are thus precursors of cholinergic false transmitters. This chapter discusses two compounds, N-methyl-N-2-hydroxyethylpyrrolidiniu (mPCh) and homocholine (HCh), using guinea-pig cortex and the electric organ of Torpedo marmorata. In the experiments with cortex, the false transmitter precursors were injected into the tissue and released transmitters collected in Locke solution applied to the surface of the cortex in plastic sleeves. Free vesicles and those attached to external membranes were isolated from tissue subjacent to the cup. Blocks of electric tissue corresponding to the territory of one nerve were perfused through the accompanying venous sinus, and vesicles isolated by the technique currently employed in our laboratory. In both cases, uptake of [ 14 C] choline and the tritiated analogue were promoted by electrical stimulation. Further stimulation caused the release of true and false transmitters in the same ratio, as they were found in a metabolically active subpopulation of vesicles even when this differed greatly from that found in the cytoplasm (brain) or whole tissue of (Torpedo).