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 M 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 increased⁴⁵Ca²⁺ 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 of⁴⁵Ca²⁺ 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 consisent 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.