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Journal of Experimental Biology 145,439-454 (1989)
Published by Company of Biologists 1989

Separation of Hydrogen Ion Currents in Intact Molluscan Neurones

M. P. MAHAUT-SMTTH ¹

¹ Department of Physiology, Medical School, University Walk, Bristol BS8 1TD; Physiological Laboratory, Downing Street, Cambridge CB2 3EG

The amplitude and rate of activation of the voltage-dependent H⁺ pathway in intact Helix neurones were investigated using standard two-electrode voltageclamp techniques. Na⁺ and K⁺ currents were inhibited by a Na⁺-free, tetraethyl-ammonium (TEA²⁺) (low-Cl^-) saline and by use of Cs⁺-filled electrodes. Ca⁺ 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 (7.4-6.9) (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.

Key words: ionic current, pH, hydrogen ion, neurone

Accepted on May 12, 1989

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