The interaction of intracellular Mg2+ and pH on C1− fluxes associated with intracellular pH regulation in barnacle muscle fibers

Abstract

The intraceilular dialysis technique was used to measure unidirectional C1− fluxes and net acid extrusion by single muscle fibers from the giant barnacle. Decreasing pHi below normal levels of 7.35 stimulated both C1− effiux and influx. These increases of C1− fluxes were blocked by disulfonic acid stilbene derivatives such as SITS and DIDS. The SITS-sensitive C1− effiux was sharply dependent upon pHi, increasing ~20-fold as pHi was decreased from 7.35 to 6.7. Under conditions of normal intracellular Mg2+ concentration, the apparent pKa for the activation of C1− effiux was 7.0. We found that raising [Mg2+]i, but not [Mg2+]0 had a pronounced inhibitory effect on both SITS-sensitive unidirectional C1− fluxes as well as on SITS-sensitive net acid extrusion. Increasing [Mg2+]i shifted the apparent pKa. of CIefflux to a more acid value without affecting the maximal flux that could be attained. This relation between pHi and [Mg2+]i on SITS-sensitive C1− effiux is consistent with a competition between H ions and Mg ions. We conclude that the SITS-inhibitable C1− fluxes are mediated by the pHi-regulatory transport mechanism and that changes of intracellular Mg2+ levels can modify the activity of the pHi regulator/anion transporter. © 1988, Rockefeller University Press., All rights reserved.