Divalent cations reduce depolarization of primary afferent terminations by GABA.

Divalent metal cations, including zinc, cadmium, cobalt, nickel, strontium, manganese, magnesium and calcium, reduced the depolarization by microelectrophoretic gamma-aminobutyric acid (GABA) and piperidine-4-sulphonic acid of the central terminations of muscle group Ia primary afferent fibres in the cat spinal cord without affecting the inhibition by GABA of the firing of spinal interneurones. There thus appears to be a difference in either the interaction of GABA with recognition sites, or in the mechanism by which such interaction activates chloride ionophores, at GABA-mediated bicuculline-sensitive synapses on the central terminals of peripheral primary afferent neurones and those on neurones located within the central nervous system.