The release of gamma‐aminobutyric acid from horizontal cells of the goldfish (Carassius auratus) retina.

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Abstract
Isolated horizontal cells from goldfish retinas were prepared by enzymatic dissociation using papain and separated from other cells by velocity sedimentation. In the intact retina, H1 horizontal cells possess a high-affinity mechanism for accumulating GABA. This property is retained in isolated cells, which also release the accumulated GABA in response to depolarization by elevated external K+. [3H]GABA release from isolated cells is unaffected by external Na+ concentrations between 20 and 120 mM. However, concentrations of 10 mM or less significantly diminishes this release, with 70% curtailed in Na+-free solutions. The results, together with morphological observations by a number of other investigators, suggest that there may be 2 distinct mechanisms for GABA release from goldfish H1 horizontal cells: one being a conventional vesicular mechanism which is Ca2+ dependent, while the other is Na+ driven and Ca2+ independent. H1 horizontal cells in the intact goldfish retina release the accumulated GABA in response to brief incubations in darkness, which is known to be the natural stimulus that depolarizes these neurons.