A tyrosine substitution in the cavity wall of a K channel induces an inverted inactivation

¹ Karolinska Institutet
² Linköpings Universitet

^* To whom correspondence should be addressed. E-mail: peter.arhem{at}ki.se.

Submitted on August 15, 2007
Revised on September 13, 2007
Accepted on 7 December 2007

	Abstract

Ion permeation and gating kinetics of voltage-gated K channels critically depend on the amino-acid composition of the cavity wall. Residue 470 in the Shaker K channel is an isoleucine, making the cavity volume in a closed channel insufficiently large for a hydrated K ion. In the cardiac hERG channel, exhibiting slow activation and fast inactivation, corresponding residue is tyrosine. To explore the role of a tyrosine at this position in the Shaker channel, we studied I470Y. The activation became slower and the inactivation faster, and more complex. At +60 mV the channel inactivated with two distinct rates (1 = 20 ms, 2 = 400 ms). Experiments with TEA and high K concentrations suggest that the slower component was of P/C-type. In addition, an inactivation component with inverted voltage-dependence was introduced. A step to -40 mV inactivates the channel with a time constant of 500 ms. Negative voltage steps do not cause the channel to recover from this inactivated state ( >> 10 min), while positive voltage steps quickly do ( = 2 ms at +60 mV). The experimental findings can be explained by a simple branched kinetic model with two inactivation pathways from the open state.

Key Words: Inactivation, S6, Shaker, Voltage-clamp, Xenopus oocytes, hERG