Intracellular acidification-induced alkali metal cation/H+ exchange in human neutrophils

Abstract

Pretreatment of isolated human neutrophils (resting pHi ≃ 7.25 at pH0 7.40) with 30 mM NH4C1 for 30 min leads to an intracellular acidification (pHi ≃ 6.60) when the NH4C1 prepulse is removed. Thereafter, in 140 mM Na+ medium, pHi recovers exponentially with time (initial rate, -0.12 pH/min) to reach the normal resting pHi by ~20 min, a process that is accomplished mainly, if not exclusively, though an exchange of internal H+ for external Na+. This Na+/H+ countertransport is stimulated by external Na+ (Km - 21 mM) and by external Li+ (Km ≃ 14 mM), though the maximal transport rate for Na+ is about twice that for Li+. Both Na+ and Li+ compete as substrates for the same translocation sites on the exchange carrier. Other alkali metal cations, such as K+, Rb+, or Cs+, do not promote pHi recovery, owing to an apparent lack of affinity for the carrier. The exchange system is unaffected by ouabain or furosemide, but can be competitively inhibited by the diuretic amiloride (Ki ≃ 8 µM). The influx of Na+ or Li+ is accompanied by an equivalent counterefflux of H+, indicating a 1:1 stoichiometry for the exchange reaction, a finding consistent with the lack of voltage sensitivity (i.e., electroneutrality) of pHi recovery. These studies indicate that the predominant mechanism in human neutrophils for pHi regulation after intracellular acidification is an amiloridesensitive alkali metal cation/H+ exchange that shares a number of important features with similar recovery processes in a variety of other mammalian cell types. © 1987, Rockefeller University Press., All rights reserved.