Topological aspects of ion transport in complex epithelia (frog skin).

A weak point of the current concept of the kinetics of ion flow in complex epithelial tissue membranes, such as frog skin, is the supposition that these tissue membranes and their exterior environments can be looked upon as a "three compartment system." In the present study a new and more realistic conceptual framework, a "multicompartment system," is applied to a computer assisted kinetic analysis of experimental data. These deal with Na+ flows in "tight" and "leaky" frog skins, prior to and after the treatment with the Na+-blocking drug amiloride. It is shown by numerical examples that unpredictable Na+ flux patterns in frog skin arise from two diverse contributing factors: 1) The constitutive physical relationships which govern the local events at the level of the plasma membranes, and 2) the much neglected topology, i.e., the "connectedness" of the heterogeneous compartments.