Separation of Hydrogen Ion Currents in Intact Molluscan Neurones Available to Purchase

The amplitude and rate of activation of the voltage-dependent H⁺ pathway in intact Helix neurones were investigated using standard two-electrode voltage clamp techniques. Na⁺ and K⁺ currents were inhibited by a Na⁺-free, tetraethylammonium (TEA⁺) (low-Cl⁻) saline and by use of Cs⁺-filled electrodes. Ca²⁺ currents were abolished by holding the membrane at –15 to –10 mV. Depolarizing voltage pulses from these low potentials activated outward currents whose tail current reversal potential shifted with changes in intracellular and extracellular pH, but not with changes in external KC1; thus these remaining currents are carried by hydrogen ions. Furthermore, the amplitude of the voltage-dependent outward current increased as the outward gradient for H⁺ was increased and a rise in pHi shifted the activation towards negative potentials. At physiological pH levels, H⁺ currents were typically 60 nA at 30 mV (cell diameter 200–250 μm). H⁺ currents were rapidly activated; the time to half maximal current at 30 mV was less than 5 ms in the pHi range tested (7·4–0·9) (pHe 7·4). The H⁺ pathway will therefore be activated by individual action potentials and may play an important role in pH homeostasis during intense neural activity.