Ammonium action on post‐synaptic inhibition in crayfish neurones: implications for the mechanism of chloride extrusion

Abstract

The reversal potential of the Cl--dependent, inhibitory post-synaptic potential [Ei.p.s.p.] was measured in the isolated crayfish [Astacus leptodactylus and A. fluviatilis] stretch receptor neuron using 2 intracellular micro-electrodes. The difference between Ei.p.s.p and the resulting membrane potential (Em), the i.p.s.p. driving force, was reversibly decreased by addition of NH3/NH4+, and the mechanism of this decrease was investigated. The i.p.s.p. driving force is maintained by a K+-Cl- co-transport mechanism, driven by the K+ gradient. The K+ site exhibits the binding selectivity: Rb+ > NH4+ > K+ > Cs+ and the mechanism is inhibited partially by frusemide and completely by DIDS [4,4-diisothiocyanostilbene -2,2-disulphonic acid].