Outward chloride/potassium co-transport in insect neurosecretory cells (DUM neurones)

The mechanism underlying outward chloride transport in the cell body and in the neuritic field of cockroach Dorsal Unpaired Median (DUM) neurones was assessed using the intracellular microelectrode technique. The chloride equilibrium potential was indirectly estimated from the reversal potentials of responses to gamma-aminobutyric acid (GABA) pressure ejections and of inhibitory postsynaptic potential (IPSP) evoked by electrical stimulation of the anterior connectives. Changes in intracellular chloride concentration [Cl-]i following various treatments were estimated from the amplitude changes of soma GABA responses and IPSP. Decreasing external Cl- concentration reduced the amplitude of GABA-mediated inhibitory events without affecting the membrane potential. Cl-/K+ co-transport was assessed by increasing external K+ concentration. The rate of outward Cl- movement was reduced furosemide but not by SITS or DIDS. All these results suggest that Cl- is not passively distributed in DUM neurones and that an active outwardly directed Cl-/K+ co-transport is implicated in the regulation of [Cl-]i.