Regulation of Cl- conductance in the thin ascending limb of Henle's loop.

Characteristics of the ion transport of the ascending thin limb of Henle's loop (ATL) were reviewed with special reference to the regulatory mechanisms of the putative Cl- channel. The ATL is highly permeable to NaCl, moderately permeable to urea, and virtually impermeable to water. The Cl- permeability is extremely high, having saturation kinetics and being inhibited by halogens. The Cl- conductances exist in series in both apical and basolateral membranes. They are inhibited by anion transport inhibitors including DIDS, phloretin, and NPPB. The Cl- conductance is pH sensitive and activated by Ca2+. NEM exhibits dual action on this conductance: irreversible inhibition and reversible stimulation. This highly effective Cl- transport system is favorable for the operation of the countercurrent multiplication system in the renal medulla.