Water Flux Coupled to Active Solute Transport Across Amphibian Epidermis

Abstract

We examine the water flux across amphibian skin driven by both the osmotic gradient and the active transport. Amphibian skin is modeled as a well-stirred compartment bounded by a mucosal barrier and a serosal barrier. The compartment represents the lateral intercellular space between cells in the stratum granulosum. The mucosal barrier is comprised of a cell barrier and a tight junctional barrier. The cell barrier is hypothesized to have the ability to actively transport solute (Na-K-ATPase) and the solute flux is assumed to satisfy the Machaelis-Menton relationship. Our model shows that: 1) there is a substantial water flux coupled to the active solute flux and this coupled water flux is nearly constant when the osmolality of the apical bathing solution is greater than 100 mOsm despite its variation; 2) the predicted rehydration rates from apical bathing solutions are in good agreement with the experiment results in Hillyard and Larsen [2]; 3) the molar ratio of the actively transported solute flux to the coupled water flux is 1:165, which is almost the same as that reported in Nielsen [5].