Modelling the control mechanism of the sodium channel in the apical membrane of tight epithelia.

In this paper it is shown th a t such behaviour may be simply modelled based on the assumption of only single occupancy of the channel. W ith use of linear flux equations the calculated flux ratio is as measured. The additional assumption of single occupancy of the channel results in the calculated values of and J qut both being multiplied by the same factor, 1 —P ,where P is the probability th a t the channel is occupied by an ion. The flux ratio thus remains unchanged but and J qut may now depend inversely upon [Na+]IN or [Na+]OUT or both, owing to the dependence of P upon these parameters. To illustrate these general conclusions, detailed calculations are made on a particular assymetrical voltage-controlled model ion channel, based upon an ordered water structure. The results obtained are shown to simulate those found experimentally for tight epithelia.