More gating charges are needed to open a Shaker K+ channel than are needed to open an rBIIA Na+ channel

Abstract

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 2.50.4. Assuming the single channel gating charge of the Shaker K+ channel to be 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.