A mathematical model of rat ascending Henle limb. II. Epithelial function

作者：Weinstein Alan M^*; Krahn Thomas A

来源：American Journal of Physiology - Renal Fluid and Electrolyte Physiology, 2010, 298(3): F525-F542.

DOI：10.1152/ajprenal.00231.2009

• NKCC
• KCC
• NHE3
• sodium transport
• potassium transport
• ammonia

Weinstein AM, Krahn TA. A mathematical model of rat ascending Henle limb. II. Epithelial function. Am J Physiol Renal Physiol 298: F525-F542, 2010. First published November 18, 2009; doi:10.1152/ajprenal.00231.2009.-A mathematical model of ascending Henle limb (AHL) epithelium has been fashioned using kinetic representations of Na(+)-K(+)-2Cl(-) cotransporter (NKCC2), KCC4, and type 3 Na(+)/H(+) exchanger (NHE3), with transporter densities selected to yield the reabsorptive Na(+) flux expected for rat tubules in vivo. Of necessity, this model predicts fluxes that are higher than those measured in vitro. The kinetics of the NKCC and KCC are such that Na(+) reabsorption by the model tubule is responsive to variation in luminal NaCl concentration over the range of 30 to 130 mM, with only minor changes in cell volume. Peritubular KCC accounts for about half the reabsorptive Cl(-) flux, with the remainder via peritubular Cl(-) channels. Transcellular Na(+) flux is turned off by increasing peritubular KCl, which produces increased cytosolic Cl(-) and thus inhibits NKCC2 transport. In the presence of physiological concentrations of ammonia, there is a large acid challenge to the cell, due primarily to NH(4)(+) entry via NKCC2, with diffusive NH(3) exit to both lumen and peritubular solutions. When NHE3 density is adjusted to compensate this acid challenge, the model predicts luminal membrane proton secretion that is greater than the HCO(3)(-)-reabsorptive fluxes measured in vitro. The model also predicts luminal membrane ammonia cycling, with uptake via NKCC2 or K(+) channel, and secretion either as NH(4)(+) by NHE3 or as diffusive NH3 flux in parallel with a secreted proton. If such luminal ammonia cycling occurs in vivo, it could act in concert with luminal K(+) cycling to facilitate AHL Na(+) reabsorption via NKCC2. With physiological ammonia, peritubular KCl also blunts NHE3 activity by inhibiting NH(4)(+) uptake on the Na-K-ATPase, and alkalinizing the cell.

• 出版日期2010-3