[Selectivity and sensitivity to blocking by hydrogen ions of batrachotoxin-modified sodium channels in nerve fiber...

Currents through normal and batrachotoxin-modified sodium channels in frog nerve were measured under voltage clamp conditions. Measured reversal potentials and the Goldman equation were used to calculate relative permeabilities. The permeability ratios were: PNa: PNH4: PK = 1: 0.47: 0.19. Hydrogen-to-sodium permeability ratio was estimated from reversal potential measurements in Na-free acid (pH 3.7-3.8) solutions. It was 528 +/- 46 for batrachotoxin-modified sodium channels. Modified channels were less sensitive to hydrogen block as compared with normal ones. The difference in apparent pKa for acid group between normal and modified channels was about 0.40.