Co-existence in DUM neurones of two GluCl channels that differ in their picrotoxin sensitivity

Whole cell patch-clamp electrophysiology was used to study the effects of L -glutamate on dissociated cockroach (Periplaneto americana) dorsal unpaired median (DUM) neurones. Application of L-glutamate via pressure-ejection pi pette resulted in a two-component hyperpolarization, consisting of an initi al transient and a second, prolonged phase. Under voltage-clamp, using isot onic chloride in the saline and intrapipette solutions, two L-glutamate-gat ed inward currents were characterized. Their reversal potentials were close to the equilibrium potential for chloride ions. One component was selectiv ely activated by ibotenate and was sensitive to picrotoxin (100 mu M), BIDN (10 mu M) and the phenylpyrazole insecticide fipronil (10 mu M), known to be potent blockers of insect GABA-gated chloride channels. The second compo nent was insensitive to picrotoxin (100 mu M) and BIDN (10 mu M). These fin dings demonstrated, for the first time, the co-existence of two pharmacolog ically distinct native insect neuronal L-glutamategated chloride channels. (C) 2000 Lippincott Williams & Wilkins.