PMID: 9551430Apr 29, 1998Paper

H+ and HCO3- transporters in the medullary thick ascending limb of the kidney: molecular mechanisms, function and regulation

Kidney International. Supplement
M Paillard

Abstract

The H+ and HCO3- transporters present in the medullary thick ascending limb (MTAL) of the kidney are involved in several functions, such as transepithelial transport, defense of cell pH and cell volume. Apical H+ secretion occurs via the NHE-3 and NHE-2 isoforms of the Na+/H+ exchanger, and H(+)-ATPase. The apical Na+/H+ exchanger is responsible for most of the apical step of transepithelial HCO3- absorption and is unresponsive to cell acidification under isosmotic conditions. Basolateral HCO3- efflux mechanisms may occur via the Cl-/HCO3- exchanger and via the cotransporters K+/HCO3- (in the rat) and Na-3HCO3- (in the mouse). However, the role of each transporter in transepithelial HCO3- absorption is currently unknown. Inhibition of the basolateral Na+/H+ exchanger (NHE-1) paradoxically inhibits the apical Na+/H+ exchanger. This cross talk is independent of cell pH and may involve variations in cell volume. Arginine vasopressin (AVP) and hyperosmolality induce a differential regulation of basolateral NHE-1 and the apical Na+/H+ exchanger. They stimulate the basolateral NHE-1, and the resulting cell alkalinization probably stimulates the pHi-sensitive AE2, which restores cell volume by cellular uptake of NaCl. They also inhibi...Continue Reading

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