An enzymatic ion exchange model for active sodium transport.

An enzymatic ion exchange model for active sodium transport is described. Kinetic equations relating net flux to time, and to concentration difference across the actively transporting membrane are derived. The second of these equations is tested, using the isolated frog skin in the "short-circuit" apparatus of Ussing. Reasonable linearity, as predicted by this equation, is observed. The passive permeability coefficient for Na(+), is calculated as 5.3 x 10(-4) +/- 5.3 x 10(-4) cm./hr. If cholinesterase is assumed to be the enzyme responsible for transport, the activity required to account for the observations reported here is 17.7 x 10(-4) mmoles/cm.(2)/hr.