Variations in the permeability properties of the inhibitory post-synaptic membrane of the crayfish neuromuscular junction when activated by different concentrations of GABA.
1. The membrane conductance of the crayfish muscle was measured with intracellular micro-electrodes. Increase in the membrane conductance induced by various concentrations of gamma-amino butyric acid (GABA) was measured in the Br(-), NO(3) (-), 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 NO(3) (-) and I(-) solutions was larger than in Cl(-) solution, while the membrane conductance activated by higher concentrations in NO(3) (-) 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(-), NO(3) (-), 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.
D000613:Aminobutyrates / Q000494:pharmacology*; D000818:Animals; D001965:Bromides / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D002712:Chlorides / Q000494:pharmacology; D003445:Crustacea; D004553:Electric Conductivity; D004558:Electric Stimulation; D004566:Electrodes; D004594:Electrophysiology; D007454:Iodides / Q000494:pharmacology; D007478:Iontophoresis; D008564:Membrane Potentials / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects*; D009566:Nitrates / Q000494:pharmacology; D013861:Thiocyanates / Q000494:pharmacology
D000613:Aminobutyrates; D001965:Bromides; D002712:Chlorides; D007454:Iodides; D009566:Nitrates; D013861:Thiocyanates