A numerical model of acid-base transport in rat distal tubule

Model Status

This CellML model is a description of Chang and Fujita's 2001 mathematical model of a Na-H exchanger in the distal tubule of the rat: it is one component of an overall model of acid/base transport in a distal tubule.

Model Structure

Acid-base transport in the rat distal tubule of the kidney has been extensively studied by a variety of different experimental methods. These experiments have shown that in the early part of the distal tubule, H⁺ is secreted into the tubular fluid via a Na/H exchanger embedded in the luminal membrane (see below). Closely linked with this process is the transport of HCO₃ ^- out of the cytosolic space into the basolateral space. This probably occurs via an anion exchanger. In the late distal tubule, distinct cell types called intercalated cells are present. These cells are specifically involved in acid-base transport. Type A cells secrete H⁺ via a luminal H-ATPase, and they extrude HCO₃ ^- via a basolateral anion exchanger. Type B cells have anion transporters on their opposite side, and they function to secrete HCO₃ ^- into the tubular fluid.

The complete original paper reference is cited below:

A numerical model of acid-base transport in rat distal tubule, Hangil Chang and Toshiro Fujita, 2001, American Journal of Physiology , 281, F222-F243. (PDF and text versions of the article are available to Journal subscribers. PubMed ID: 11457714)

State diagram of the Na-H exchanger. In this model, the Na-H exchanger has a single binding site (E) to which Na+, H+, and NH4 + bind competitively. Only the bound forms of the transporter are able to cross the membrane. (Symbols with the asterisk (*) represent conformations facing the cytosol, symbols without indicate conformations facing the extracellular environment.)