DIFFERENTIAL ACETYLCHOLINE AND GABA RELEASE FROM CULTURED CHICK RETINA CELLS

In the present work we investigated the mechanisms controlling the rel ease of acetylcholine (ACh) and of gamma-aminobutyric acid (GABA) from cultures of amacrine-like neurons, containing a subpopulation of cell s which are simultaneously GABAergic and cholinergic. We found that 81 .2 +/- 2.8% of the cells present in the culture were stained immunocyt ochemically with an antibody against choline acetyltransferase, and 38 .5 +/- 4.8% of the cells were Stained with an antibody against GABA. M ost of the cells containing GABA (87.0 +/- 2.9%) were cholinergic. The release of acetylcholine and GABA was mostly Ca2+-dependent, although a significant release-of [H-3]GABA occurred by reversal of its transp orter. Potassium evoked the Ca2+-dependent release of [H-3]GABA and [H -3]acetylcholine, with EC50 of 31.0 +/- 1.0 mM and 21.6 +/- 1.1 mM, re spectively. The Ca2+-dependent release of [H-3]acetylcholine was signi ficantly inhibited by 1 mu M tetrodotoxin and by low (30 nM) omega-con otoxin GVIA (omega-CgTx GVIA) concentrations, or by high (300 nM) nitr endipine (Nit) concentrations, On the contrary, the release of [C-14]G ABA was reduced by 30 nM nitrendipine, or by 500 nM omega-CgTx GVIA, b ut not by this toxin at 30 nM. The release of either transmitters was unaffected by 200 nM omega-Agatoxin IVA (omega-Aga IVA), a toxin that blocks P/Q-type voltage-sensitive Ca2+ channels (VSCC). The results sh ow that Ca2+-influx through omega-CgTx GVIA-sensitive N-type VSCC and through Nit-sensitive L-type VSCC induce the release of ACh and GABA. However, the significant differences observed regarding the Ca2+ chann els involved in the release of each neurotransmitter suggest that in a macrine-like neurons containing simultaneously GABA and acetylcholine the two neurotransmitters may be released in distinct regions of the c ells, endowed with different populations of VSCC.