Effects of the ionophores X537A and A23187 on GABA, glycine, and taurine release from chick retinal subcellular fractions.

The ionophore X537A at concentrations of 5--20 microM stimulated the release of [3H]GABA and [35S]taurine from retinal subcellular crude nuclear (P1) and crude synaptosomal (P2) fractions. The release of [3H]GABA increased 114% and 136% over control values in P1 and P2 fractions, respectively. The efflux of [35S]taurine from P1 was increased by 45% and that from P2 by 21%. X537A increased 45Ca2+ uptake in the P2 fraction but not in the P1 fraction. The effect of X537A on the amino acid release was not dependent on the presence of exogenous calcium. X537A did not affect [3H]GABA or [35S]taurine uptake by the retinal fractions. A23187 enhanced [3H]GABA release from P1 and P2 by 52% and 105%, respectively. The ionophore also increased [14C]glycine liberation in both P1 (35%) and P2 (50%) but failed to stimulate [35S]taurine release. A23187 produced a transient increase of 45Ca2+ uptake of 38% in P1 and 30% in P2. The effects of A23187 on the release of amino acids were calcium dependent. The amino acid uptake was not affected by the ionophore. These results are consistent with the suggested neurotransmitter role for GABA at the outer synaptic layer and for GABA and glycine at the inner synaptic layer of the retina. A neurotransmitter role for taurine is not supported by the present results.