Cooperative effects in models of steady-state transport across membranes. I.

Three simple models are discussed which show cooperative effects in the steady-state transport of neutral molecules across a membrane. The Bragg-Williams approximation is employed, and its limitations discussed. In this approximation to cooperative problems, the diagram method for the calculation of steady-state probabilities and fluxes can still be used. This paper is closely related to one by Blumenthal, Changeux, and Lefever, and provides the foundation for sequels on an oscillatory steady-state phase-transition model (part II) and on simple models possibly related to steady-state potassium ion transport across a nerve membrane (part III).