Ammonium and chloride extrusion: hyperpolarizing synaptic inhibition in spinal motoneurons.

The reversal potential of postsynaptic inhibition shifts toward resting membrane potentials in cat spinal motoneurons after intravenous infusion of ammonium salts(1 to 3 millimoles per kilogram of body weight). Simultaneously, the depolarizing action of intracellularly injected chloride ions on the inhibitory membrane is enhanced and recovery therefrom is prolonged. Passive membrane properties remain unaltered. The results indicate a blocking of active extrusion of chloride which normally maintains a high ionic gradient for hyperpolarizing inhibition.