Stability of the Shab K+ channel conductance in 0 K+ solutions: the role of the membrane potential.
Shab channels are fairly stable with K(+) present on only one side of the membrane. However, on exposure to 0 K(+) solutions on both sides of the membrane, the Shab K(+) conductance (G(K)) irreversibly drops while the channels are maintained undisturbed at the holding potential. Herein it is reported that the drop of G(K) follows first-order kinetics, with a voltage-dependent decay rate r. Hyperpolarized potentials drastically inhibit the drop of G(K). The G(K) drop at negative potentials cannot be explained by a shift in the voltage dependence of activation. At depolarized potentials, where the channels undergo a slow inactivation process, G(K) drops in 0 K(+) with rates slower than those predicted based on the behavior of r at negative potentials, endowing the r-V(m) relationship with a maximum. Regardless of voltage, r is very small compared with the rate of ion permeation. Observations support the hypothesized presence of a stabilizing K(+) site (or sites) located either within the pore itself or in its external vestibule, at an inactivation-sensitive location. It is argued that part of the G(K) stabilization achieved at hyperpolarized potentials could be the result of a conformational change in the pore itself.
Gómez-Lagunas
Froylán
F
Facultad de Medicina, Dept. Fisiologia, Universidad Nacional Autónoma de México, Ciudad Universitaria, Apartado Postal 70-250 Mexico D.F. 04510, Mexico. froylangl@yahoo.com
D000818:Animals; D002460:Cell Line; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D051669:Shab Potassium Channels / Q000502:physiology*; D018411:Spodoptera / Q000378:metabolism*
D051669:Shab Potassium Channels; D011188:Potassium
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