A THERMODYNAMIC ANALYSIS OF PARTICLE FLOW THROUGH BIOLOGICAL MEMBRANES

The methods of irreversible thermodynamics are applied to the problem of particle flow through biological membranes. Formulae are derived for the unidirectional flux and flux ratio of a permeant species under conditions where there is a coupling between flows and between flows and metabolism. The flux ratio formula is shown to be useful under appropriate conditions, for providing evidence antagonistic to the hypothesis of active transport of the permeant species. A relation is derived which specifies the conditions under which the use of tracers should lead to accurate estimates of unidirectional fluxes. When the treatment is applied to the problem of water flow through an inert semipermeable membrane a particularly simple formula is obtained for the ratio of the permeability coefficients for water as determined osmotically and isotopically. © 1969.