Structural and functional properties of the novel heteromeric hSK1-hIKCa channel

Abstract

Calcium-activated potassium (KCa) channels couple changes in calcium ion (Ca²⁺) concentration, which commonly increases during periods of membrane or cellular excitability, to potassium ion (K⁺) efflux that brings about a relaxation or change in cellular volume. Small-conductance KCa (SK) channels have been proposed to mediate certain KCa components of the repolarising potentials of neurons and cardiac cells. The expression of intermediate-conductance KCa (IKCa) channels has been proposed overlap with that of SK channels, and SK and IKCa channels have now been shown to preferentially co-assemble to form heteromeric hSK1-hIKCa channels. This implicates these heteromers in physiological roles that might have previously been attributed to other homomeric or heteromeric SK channels. Due to this, it is important to understand the structural and functional characteristics of heteromeric hSK1-hIKCa channels.
C-terminal coiled-coil domains (CCDs) have been proposed to mediate SK channel assembly. Site-directed mutagenesis was used to substitute the H389 residue within the second C-terminal CCD of hIKCa subunits to a glutamate residue. Outside-out patch clamp electrophysiology and pharmacological investigations revealed that this mutation disrupted but not prevent the formation of heteromeric hSK1-hIKCa channels, while having no affect upon the formation of homomeric hIKCa channels. These findings support the idea that the preferential formation of heteromeric hSK1-hIKCa channels is highly specific. Also, inside-out patch clamp was used to investigate the Ca²⁺ sensitivity of homomeric hSK1 and hIKCa as well as heteromeric hSK1-hIKCa channels. Compared to the Ca²⁺ sensitivities of both homomeric hSK1 and hIKCa channels, the Ca²⁺ sensitivity of heteromeric hSK1-hIKCa channels was found to be significantly right-shifted. These findings support the proposal that these channels are a novel member of the KCa family, with distinct functional properties that could be an indication that they play a distinct physiological role.

Date of Award	2 Dec 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Neil Marrion (Supervisor) & David N Sheppard (Supervisor)