Proton currents in human eosinophils. Schrenzel, Jacques, Daniel P. Lew, and Karl-Heinz Krause. Division of Infectious Diseases, Department of Medicine, University Hospital, 1211 Geneva 14, Switzerland
APStracts 3:0205C, 1996.
The killing of metazoan parasites by eosinophils involves the activation of a respiratory burst oxidase. To investigate whether human eosinophils possess an H+ conductance, that might participate in the extrusion of H+ ions generated by the respiratory burst, we employed the whole cell patch-clamp technique under conditions designed to isolate putative H+ currents. We observed a slow activation of outward currents by depolarizing voltage steps. The reversal potential of the currents was a function of the H+ gradient, demonstrating that the current was carried by H+ ions. The H+ conductance was activated by cytosolic acidification and reversibly blocked by divalent and trivalent cations. During large prolonged depolarizing voltage steps, the current activation was followed by a decrease in current. This was due to cytosolic H+ ion depletion as evidenced by: i) a change in reversal potential, and ii) a cytosolic alkalization. We also observed a rundown of the current, possibly due to the loss of a cytosolic factor necessary for H+ current activity. An elevated pipette [Ca2+] (1?[mu]M) activated the H+ conductance, suggesting that the cytosolic [Ca2+] is involved in the physiological regulation of H+?currents. The Ca2+-activated currents had properties similar to the currents observed at low Ca2+ concentrations (reversal potential, high affinity block by Zn2+, kinetics of tail currents, kinetics of rundown). The Ca2+ effect might be mediated by phospholipase A2 as: i)?the currents were also activated by arachidonic acid, ii)?the Ca2+ effect and the arachidonic acid effect were not additive, and iii)?the Ca2+ effect, but not the arachidonic acid effect, was blocked by a phospholipase A2 inhibitor. Taken together, our results demonstrate that human eosinophils have large H+ currents which are activated by physiological intracellular signals. The electrophysiological properties of the H+ currents and their regulation strongly suggest that they participate in H+ extrusion during the respiratory burst. 

Received 1 November 1995; accepted in final form 19 June 1996.
APS Manuscript Number C695-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96