Ion channel activity from the midgut brush-border membrane of gypsy moth (Lymantria dispar) larvae

Ion channels from the midgut apical membrane of gypsy moth (Lymantria dispa r) larvae were studied following mechanical fusion of brush-border membrane vesicles with planar phospholipid bilayer membranes. In symmetrical 300 mm ol l(-1) KCl (pH 9.0), nine different channels with conductances ranging fr om 27 to 795 pS and linear current/voltage relationships were resolved. In the presence of a KCl gradient across the bilayer (450 mmol l(-1) cis/150 m mol l(-1) trans), 11 different conductance levels ranging from 16 to 850 pS were detected. The channels were slightly cationic: the zero-current rever sal potential was shifted by -5 mV to -21 mV compared with symmetrical KCl conditions, corresponding to p(K)/p(Cl) permeability ratios of 1.5-8.0. Mos t channels were neither voltage-dependent nor Ca2+-sensitive and displayed complex gating kinetics. Addition of Ba2+ or Cs+ to both sides of the bilay er had little effect on channel activity, but fewer distinct channels were observed when KCl was replaced by potassium gluconate, suggesting an effect of Cl- on channel activity. A reduced number of channels was also detected when KCl was replaced by N-methyl-D-glucamine-HCl. Under asymmetrical N-me thyl-D-glucamine-HCl conditions, only anionic channels were observed. They exhibited current rectification (35 pS at negative voltages and 81 pS at po sitive voltages) and were strongly voltage-dependent.