More gating charges are needed to open a Shaker K+ channel than are needed to open an rBIIA Na+ channel.
This study presents what is, to our knowledge, a novel technique by means of which the ratio of the single gating charges of voltage-gated rat brain IIA (rBIIA) sodium and Shaker potassium ion channels was estimated. In the experiment, multiple tandems of enhanced green fluorescent protein were constructed and inserted into the C-terminals of Na(+) and K(+) ion channels. cRNA of Na(+) and K(+) ion channels was injected and expressed in Xenopus laevis oocytes. The two electrode voltage-clamp technique allowed us to determine the total gating charge of sodium and potassium ion channels, while a relative measure of the amount of expressed channels could be established on the basis of the quantification of the fluorescence intensity of membrane-bound channels marked by enhanced green fluorescent proteins. As a result, gating charge and fluorescence intensity were found to be positively correlated. A relative comparison of the single gating charges of voltage-gated sodium and potassium ion channels could thus be established: the ratio of the single gating charges of the Shaker potassium channel and the rBIIA sodium channel was found to be 2.5 +/- 0.4. Assuming the single channel gating charge of the Shaker K(+) channel to be approximately 13 elementary charges (well supported by other studies), this leads to approximately six elementary charges for the rBIIA sodium channel, which includes a fraction of gating charge that is missed during inactivation.
Gamal El-Din
Tamer M
TM
University of Zürich, Institute of Physiology, 8057 Zürich, Switzerland.
Grögler
Dominik
D
Lehmann
Claudia
C
Heldstab
Hansjakob
H
Greeff
Nikolaus G
NG
D000818:Animals; D002478:Cells, Cultured; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D051637:Shaker Superfamily of Potassium Channels / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure; D015222:Sodium Channels / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure; D055672:Static Electricity; D014982:Xenopus laevis
D051637:Shaker Superfamily of Potassium Channels; D015222:Sodium Channels