The multi-ion nature of the pore in Shaker K%2b channels Article uri icon

abstract

  • We have investigated some of the permeation properties of the pore in Shaker K channels. We determined the apparent permeability ratio of K%2b, Rb%2b, and NH4%2b ions and block of the pore by external Cs%2b ions. Shaker channels were expressed with the baculovirus/Sf9 expression system and the channel currents measured with the whole-cell variant of the patch clamp technique. The apparent permeability ratio, PRb/PK, determined in biionic conditions with internal K%2b, was a function of external Rb%2b concentration. A large change in PRb/PK occurred with reversed ionic conditions (internal Rb%2b and external K%2b). These changes in apparent permeability were not due to differences in membrane potential. With internal K%2b, PNH4/PK was not a function of external NH4%2b concentration (at least over the range 50–120 mM). We also investigated block of the pore by external Cs%2b ions. At a concentration of 20 mM, Cs%2b block had a voltage dependence equivalent to that of an ion with a valence of 0.91; this increased to 1.3 at 40 mM Cs%2b. We show that a 4-barrier, 3-site permeation model can simulate these and many of the other known properties of ion permeation in Shaker channels. © 1994, The Biophysical Society. All rights reserved.

publication date

  • 1994-01-01