Na(+) interaction with the pore of Shaker B K(+) channels: zero and low K(+) conditions.
The Shaker B K(+) conductance (G(K)) collapses (in a reversible manner) if the membrane is depolarized and then repolarized in, 0 K(+), Na(+)-containing solutions (Gómez-Lagunas, F. 1997. J. Physiol. 499:3-15; Gómez-Lagunas, F. 1999. Biophys. J. 77:2988-2998). In this work, the role of Na(+) ions in the collapse of G(K) in 0-K(+) solutions, and in the behavior of the channels in low K(+) was studied. The main findings are as follows. First, in 0-K(+) solutions, the presence of Na(+) ions is an important factor that speeds the collapse of G(K). Second, external Na(+) fosters the drop of G(K) by binding to a site with a K(d) = 3.3 mM. External K(+) competes, in a mutually exclusive manner, with Na(o)(+) for binding to this site, with an estimated K(d) = 80 microM. Third, NMG and choline are relatively inert regarding the stability of G(K); fourth, with [K(o)(+)] = 0, the energy required to relieve Na(i)(+) block of Shaker (French, R.J., and J.B. Wells. 1977. J. Gen. Physiol. 70:707-724; Starkus, J.G., L. Kuschel, M. Rayner, and S. Heinemann. 2000. J. Gen. Physiol. 110:539-550) decreases with the molar fraction of Na(i)(+) (X(Na,i)), in an extent not accounted for by the change in Delta(mu)(Na). Finally, when X(Na,i) = 1, G(K) collapses by the binding of Na(i)(+) to two sites, with apparent K(d)s of 2 and 14.3 mM.
Gómez-Lagunas
F
F
Departamento de Fisiología, Facultad de Medicina, UNAM, Universitaria, México City 04510, México. froylan@ibt.unam.mx
D000818:Animals; D016367:Baculoviridae; D002460:Cell Line; D004594:Electrophysiology; D007313:Insecta; D007477:Ions; D008564:Membrane Potentials / Q000502:physiology; D011188:Potassium / Q000737:chemistry / Q000493:pharmacokinetics; D015221:Potassium Channels / Q000502:physiology*; D051637:Shaker Superfamily of Potassium Channels; D012964:Sodium / Q000737:chemistry*
D007477:Ions; D015221:Potassium Channels; D051637:Shaker Superfamily of Potassium Channels; D012964:Sodium; D011188:Potassium