Baseline Properties of Slo1 K+ (BK) Channels Without the Gating Ring

Abstract

High conductance Ca2+- and voltage-activated K+ (Slo1 or BK) channels have two functional domains: a “core” consisting of four voltage sensors controlling an ion-conducting pore, and a larger “tail” that forms an intracellular gating ring thought to confer Ca2+ and Mg2+ sensitivity. Whereas the modular structure is known, the properties of the individual modules and the transduction pathways among the modules are poorly understood because it has not been possible to study the core in isolation. To approach this problem, we developed novel constructs that allow functional cores of Slo1 channels to be expressed in the absence of the gating ring. One of these constructs replaced the 827 amino acid gating ring with a short synthetic peptide of 11 amino acids to enhance synthesis and surface expression. Functional expression of this construct in Xenopus oocytes produced currents from channels that: displayed voltage activation with a right-shifted G-V relation; lacked Ca2+ and Mg2+ sensitivity; exhibited a six-fold reduction in mean open interval and burst duration; had an apparent ∼30% reduction in single-channel conductance; and were blocked by extracellular iberiotoxin and TEA and displayed slowed kinetics when co-expressed with β1 subunits. The extent to which any altered channel properties when compared to WT channels reflect the absence of allosteric input from the gating ring, revealing the baseline properties of the core, or reflect input from the 11 amino acid replacement tail is under investigation. Supported in part by NS061871 to LS and AR032805 to KLM.