Ionic mechanism of the H⁺ pump in a snail neurone

Abstract

THE observed values of pH inside nerve and muscle cells are too high to be explained by a passive distribution of H⁺ across the cell membrane^1–4. Thus there is believed to be a system, provisionally named a H⁺ or proton pump, which transports H⁺ out of, or OH⁻ or HCO₃⁻ into the cell. In spite of its importance, little is known about this system, perhaps because it cannot easily be studied using radioisotopes, the use of which has yielded much information about the far better known Na pump. One way the H⁺ pump can be investigated is by following intracellular pH (pH_i) with a pH-sensitive microelectrode: because a similar Na⁺-sensitive microelectrode can be used to study the Na pump, it is also possible to compare the two pumps in the same preparation using essentially the same methods. Thus the recessed-tip type of pH-sensitive³ or Na⁺-sensitive⁵ microelectrode can be used to record pH_i or intracellular Na⁺ ([Na⁺]_i) in cells, such as snail neurones, which are tough enough to permit intracellular iontophoretic injections of acid or Na salts. I report here experiments in which the mechanism of the H⁺ pump has been investigated by comparing the response of pH_i to HCl injection with the response of [Na⁺]_i to NaCl injection.