pH regulation in single glomerular mesangial cells. II. Na+-dependent and -independent Cl(-)-HCO3- exchangers.
We used the pH-sensitive dye 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) to further characterize the mechanisms of intracellular pH (pHi) regulation in renal mesangial cells. In the accompanying paper [Am. J. Physiol. 255 (Cell Physiol. 24): C844-C856, 1988], we showed that acid extrusion from mesangial cells is mediated by both an ethylisopropylamiloride (EIPA)-sensitive Na+-H+ exchanger and a 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS)-sensitive-HCO3(-)-dependent mechanism. In this study, we examined the ionic dependencies of pHi-regulatory mechanisms in the presence of CO2-HCO3-. We found that in CO2-HCO3-, approximately 90% of the net acid extrusion occurring during recovery from an acid load is blocked by removing external Na+. Short-term (less than 15 min) removal of external Cl- has little effect on the rate of recovery in CO2-HCO3-. In contrast longer periods of external Cl- removal (1-2 h) blocks 40-60% of the rate of recovery, which is consistent with the hypothesis that a large fraction of the SITS-sensitive-HCO3(-)-dependent recovery mechanism described in the preceding paper is also Na+- and Cl(-)-dependent. Therefore, this Cl(-)-dependent component is probably mediated by a Na+-dependent Cl(-)-HCO3- exchanger. As much as 16% of total acid extrusion is insensitive to EIPA and long-term Cl- removal but is blocked by SITS. Thus either 1-2 h of Cl- removal is insufficient to wash out all internal Cl-, or a small component of acid extrusion is mediated by a Cl(-)-independent mechanism, such as the electrogenic Na+/HCO3- cotransporter. We also studied the effect on pHi of the removal and readdition of external Cl-, observing pHi changes consistent with the existence of a Na+-independent Cl(-)-HCO3- exchanger, which would presumably function as an acid loader. In contrast to the Na+-H+ exchanger and Na+-dependent Cl(-)-HCO3- exchanger, which are stimulated at low pHi, the Cl(-)-HCO3- exchanger is stimulated at high pHi. Thus the acid-extruding and acid-loading mechanisms have opposite pHi dependencies.
Boyarsky
G
G
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
Ganz
M B
MB
Sterzel
R B
RB
Boron
W F
WF
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000409:Alanine / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002413:Cations, Divalent; D002478:Cells, Cultured; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000494:pharmacology*
D002352:Carrier Proteins; D002413:Cations, Divalent; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D008565:Membrane Proteins; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D012964:Sodium; D005947:Glucose; D000409:Alanine; C039614:ethylisopropylamiloride