ABSTRACT
In all animal cells, the presence of nondiffusible anions in the intracellular compartment creates a Gibbs-Donnan equilibrium which tends to produce colloid-osmotic swelling. Such a swelling is prevented by so-called mechanisms of cell volume maintenance. In addition, epithelial cells face unique and potentially severe challenges for cell volume regulation during changes in transport rate. “Homocellular” regulatory mechanisms are intrinsic mechanisms set to maintain cell volume and composition in the face of changes in transepithelial transport rate. Amiloride addition to the solution bathing the apical surface of toad or frog urinary bladder epithelium induces a rapid fall in basolateral membrane conductance with no change in cell volume. In conclusion, the results discussed in this section provide convincing demonstration of several instances of cross-talk in tight epithelia. In a later section we will discuss the sensing and transduction systems involved in these responses.
