Abstract
1. The membrane conductance of the crayfish muscle was measured with intracellular micro-electrodes. Increase in the membrane conductance induced by various concentrations of γ-amino butyric acid (GABA) was measured in the Br-, NO3-, I- and CNS- solutions and compared with that in Cl- solution. When the membrane was activated by lower concentrations of GABA, the resulting membrane conductance in NO3- and I- solutions was larger than in Cl- solution, while the membrane conductance activated by higher concentrations in NO3- and I- solutions were smaller than in Cl- solution. The membrane conductance activated by GABA was larger in Br- solution and smaller in CNS- solution than the membrane conductance activated in Cl- solution, throughout the concentration range of GABA examined.
2. The reversal potential of inhibitory junctional potentials (i.j.p.s) was measured shortly after replacing Cl- by foreign anions: Br-, NO3-, I- and CNS-. In I- solution the i.j.p.s produced by lower stimulation frequencies showed a reversal potential at a more hyperpolarized level than those produced by higher stimulation rates.
3. Shortly after replacing Cl- by I-, the GABA potential induced by iontophoretic application showed a triphasic potential change at the `reversal' potential. The reversal level of the GABA potential produced by smaller doses was at a more hyperpolarized level than that produced by larger doses.
4. Possibilities of a concentration effect of GABA are discussed. It is suggested that the relative permeability of the crayfish inhibitory membrane to anions changes depending on the concentration of GABA.
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Selected References
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