Basolateral membrane Cl⁻-, Na⁺-, and K⁺-coupled base transport mechanisms in rat MTALH

Abstract

Mechanisms involved in basolateral HCO[Formula: see text] transport were examined in the in vitro microperfused rat medullary thick ascending limb of Henle (MTALH) by microfluorometric monitoring of cell pH. Removing peritubular Cl− induced a cellular alkalinization that was inhibited in the presence of peritubular 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) and blunted in the absence of external CO2/HCO[Formula: see text]. The alkalinization elicited by removing peritubular Cl−persisted in the bilateral absence of Na+, together with a voltage clamp. When studied in Cl−-free solutions, lowering peritubular pH induced a base efflux that was inhibited by peritubular DIDS or by the absence of external CO2/HCO[Formula: see text]. Removing peritubular Na+ elicited a cellular acidification that was accounted for by stimulation of a DIDS- and ethylisopropylamiloride (EIPA)-insensitive Na+-HCO[Formula: see text] cotransport and inhibition of a basolateral Na+/H+exchange. Increasing bath K+ induced an intracellular alkalinization that was inhibited in the absence of external CO2/HCO[Formula: see text]. At 2 mM, peritubular Ba2+, which inhibits the K+-Cl−cotransport, did not induce any change in transepithelial voltage but elicited a cellular alkalinization and inhibited K+-induced cellular alkalinization, consistent with the presence of a basolateral, electroneutral Ba2+-sensitive K+-Cl− cotransport that may operate as a K+-HCO[Formula: see text] cotransport. This cotransport was inhibited in the peritubular presence of furosemide, [(dihydroindenyl)oxy]alkanoic acid, 5-nitro-2-(3-phenylpropylamino)benzoate, or DIDS. At least three distinct basolateral HCO[Formula: see text] transport mechanisms are functional under physiological conditions: electroneutral Cl−/HCO[Formula: see text] exchange, DIDS- and EIPA-insensitive Na+-HCO[Formula: see text] cotransport, and Ba2+-sensitive electroneutral K+-Cl−(HCO[Formula: see text]) cotransport.

Regulation of the Cl−/HCO3 − Exchanger AE2 in Rat Thick Ascending Limb of Henle’s Loop in Response to Changes in Acid-Base and Sodium Balance

“…In two studies using basolateral membrane vesicles isolated from a purified MTAL tubule suspension, we previously demonstrated that the main basolateral HCO 3 Ϫ efflux pathway in MTAL cells is via Cl Ϫ /HCO 3 Ϫ exchange activity attributable to AE2 (12,13). An additional study from our laboratory confirmed in isolated, intact, microperfused MTAL that the main basolateral bicarbonate efflux pathway was Cl Ϫ dependent, Na ϩ independent, and 4,4Ј-diisothiocyanostilbene-2,2Ј-disulfonic acid (DIDS) sensitive, properties shared with AE2 (16).…”

Nongenomic regulation by aldosterone of the epithelial NHE3 Na+/H+ exchanger

“…Although the fractional inhibition by aldosterone was slightly lower in the presence of luminal DIDS, we are hesitant to ascribe any physiological significance to this because it is the result of an increase in basal HCO 3 Ϫ absorption rate observed when apical K ϩ -HCO 3 Ϫ cotransport is inhibited (39). Nevertheless, our results do not conclusively rule out that an effect of aldosterone to increase apical K Ϫ transport pathways (5,6,31). In keeping with its central role in the maintenance of sodium, volume, and acid-base balance, NHE3 is regulated acutely by several important factors, including catecholamines, angiotensin II, endothelin, dopamine, and growth factors (2,25,32,42).…”

The Na+-dependent chloride-bicarbonate exchanger SLC4A8 mediates an electroneutral Na+ reabsorption process in the renal cortical collecting ducts of mice

“…Intracellular pH was monitored using the pH-sensitive dye BCECF (29). Intracellular dye was calibrated at the end of each experiment using the high-[K + ]/nigericin technique (48). Briefly, tubules were perfused and bathed with a HEPES-buffered, 95-mM K + solution containing 10 μM of the K + /H + exchanger nigericin.…”