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Journal of Experimental Biology 145,455-464 (1989)
Published by Company of Biologists 1989

The Effect of Zinc on Calcium and Hydrogen Ion Currents in Intact Snail Neurones

M. P. MAHAUT-SMITH ¹

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

The effects of external Zn²⁺ on Ca²⁺ and H⁺ currents in the soma of intact Helix neurones were investigated using standard two-electrode voltage-clamp procedures. Cells were exposed to a 0Na⁺, tetraethylammonium (TEA⁺) saline and clamped with Cs⁺-filled electrodes, which allows separation of voltagedependent H⁺ and Ca²⁺ currents using different holding potentials. Outward H⁺ currents, activated by depolarizations from holding potentials in the range -15 to -10 mV, were rapidly blocked by low concentrations of external Zn²⁺ with a Kd of approximately 16µmol l^-1. H⁺ current activation was also markedly slowed and the block was slow to reverse. Ca²⁺ currents, largely free from contamination by outward current, were activated by small depolarizations from a holding potential of -55 mV. Ca²⁺ currents were reduced by Zn²⁺, but the K_d for block was more than 80 times greater than for block of H⁺ currents. Thus, low concentrations of Zn²⁺ provide a method of selectively inhibiting H⁺ current in studies of Ca²⁺ current. This was demonstrated in cells which slowly acidified following exposure to 0Na⁺, TEA⁺ saline, leading to an increased outward H⁺ current. Washing with low concentrations of Zn²⁺ blocked the H⁺ current and uncovered the underlying Ca²⁺ current. The results also suggest that Zn²⁺ will be a useful tool in studies of the physiological role of the H⁺ pathway.

Key words: zinc, calcium current, hydrogen ion

Accepted on May 12, 1989