The interaction of intracellular Mg2+ and pH on Cl- fluxes associated with intracellular pH regulation in barnacle muscle fibers.
The intracellular dialysis technique was used to measure unidirectional Cl- fluxes and net acid extrusion by single muscle fibers from the giant barnacle. Decreasing pHi below normal levels of 7.35 stimulated both Cl- efflux and influx. These increases of Cl- fluxes were blocked by disulfonic acid stilbene derivatives such as SITS and DIDS. The SITS-sensitive Cl- efflux was sharply dependent upon pHi, increasing approximately 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 Cl- efflux was 7.0. We found that raising [Mg2+]i, but not [Mg2+]o, had a pronounced inhibitory effect on both SITS-sensitive unidirectional Cl- fluxes as well as on SITS-sensitive net acid extrusion. Increasing [Mg2+]i shifted the apparent pKa of Cl- efflux to a more acid value without affecting the maximal flux that could be attained. This relation between pHi and [Mg2+]i on SITS-sensitive Cl- efflux is consistent with a competition between H ions and Mg ions. We conclude that the SITS-inhibitable Cl- 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.
Russell
J M
JM
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
Brodwick
M S
MS
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism; D001468:Thoracica / Q000378:metabolism*
D002712:Chlorides; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D008274:Magnesium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid