ScienceAsia 9 (1983): 153-174 |doi: 10.2306/scienceasia1513-1874.1983.09.153

MODIFICATION OF ³H--AMINOBUTYRIC ACID (³H-GABA) UPTAKE AND RELEASE BY ACETYLCHOLINE (ACh) IN SYNAPTOSOMAL FRACTIONS OF RABBIT RETINA

DIANNA A. REDBURN and THYON CHENTANEZ^a

ABSTRACT: In retinal outer plexiform layer (OPL) synaptosomal fraction (P₁), photoreceptor terminals have pre-and postsynaptic elements of the triad attached. In retinal inner plexiform layer (IPL) synaptosomal fraction (P₂), serial and reciprocal synapses are abundant. Thus, OPL and IPL fractions obtained from the retina are highly suitable for a direct, biochemical analysis of presynaptic receptor mechanism. In these studies, modifications in uptake and release of a given neurotransmitter were monitored after exposure to various concentrations of other neurotransmitters. One of the most pronounced effects was the stimulation of ³H--aminobutyric acid (³H-GABA) uptake and release in OPL synaptosomes by acetyl choline (Ach), Aspartate (Asp) and dopamine (DA) did not modify ³H-GABA uptake of IPL and OPL, and ACh did not change the ³H-GABA uptake of IPL synaptosomes. Furthermore, the increase in ³H-GABA uptake of OPL caused by ACh was mediated by an increase in the maximal velocity, Vmax, with no change in the affinity (K_T) of the uptake system for GABA. ³H-GABA uptake of OPL was also increased by preincubation with choline (Ch), a precursor of ACh; by neostigmine, an acetylcholinesterase (AChE) inhibitor; and by nicotine and 1,1-dimethyl-4-phenylpiperazinium (DMPP), nicotinic cholinergic receptor agonists.

The effect of Ch preincubation on the increase in OPL synaptosomal uptake of ³H-GABA was blocked by hemicholinium-3 (HC-3), hexamethonium, mecamylamine, d-tubocurarine, (-) scopolamine and atropine. The concentrations of the nicotinic cholinergic receptor blockers need,ed to inhibit cholinergic stimulation by 50 % (IC₅₀) were lower than those needed for the muscarinic blockers.

PI Ch preincubotion and the addition of ACh into the perfusion medium also enhanced Ca⁺⁺dependent ³H-GABA release from the OPL synoptosomes.

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Department of Neurobiology and Anatomy, the University of Texas Medical School at Houston, Houston, Texas 77025, USA. and ^a Physiology Department, Faculty of Science, Mahidol University, Rama VI Rd., Bangkok, 10400 Thailand.

Received 3 February 1983