Open Channels Selectivity and Conductance

Similar experiments were carried out for the potassium channel/ It has been shown, for instance, that PfiJPK = 0.010. The investigation of a number of cations with different crystallographic radii made it possible to estimate the cross-sectional area of the selective filter region of the potassium channel to be ca. 3 A in diameter. 

Earlier we noted that sodium channels have a very high conductance. When open, the flux through such a channel is ca. lO ions per second. One may therefore ask, is it not ion diffusion in the vicinity of membrane that limits the process Estimates show that the maximum diffusion flux is about one order of magnitude higher than the measured current, i.e., the intramembrane transport is the dominant process. This is all the more true for potassium channels whose conductance is ca. 10 ions per second. 

The experimental data suggest that under physiological conditions where sodium ions travel through the sodium channel the inward and outward fluxes 

The next problem is to calculate the basic equilibrium and process rate data for a membrane containing channels of a specific type. All these para- 

Under these assumptions the set of equations (118) has a solution of the form  

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