Pharmacology & regulation of Slo2 and Slo3 potassium channels

Large-conductance-Ca2+-activated potassium Slo1 channels are well characterised members of the Slo channel family. The other members, Slo3 and Slo2.χ, are less characterised and their physiological roles are elusive. Little is known of the pH-sensitive Slo3 channel, aside from a role regulating Ca2+ influx through CatSper channels during capacitation in spermatozoa. This thesis aims to investigate mSlo3 pharmacology and determine if mSlo3-
EST’s encode novel isoforms. Na+-activated Slo2.χ channels (Slo2.1/Slo2.2) are thought to mediate adaptation of neuronal action potential firing rate and slow after hyperpolarisations following repetitive firing. We aim to characterise hSlo2.2a currents and their bithionol sensitivity, an activator of a rat isoform.

Mutation of the conserved phenylalanine in the S6-domain (mSlo3-F304/hSlo1-F380) to tyrosine has similar effects on Slo channels, namely a negative shift in the voltagedependence of activation and an increase in membrane conductance. mSlo3 pharmacology matches the IKSper profile and suggests roles for mSlo3 as a pharmacological target in
infertility treatment. This work identified a novel splice-variant of mSlo3; CV562866 lacks transmembrane domains and is more widely expressed than mSlo3. CV562866 protein is
expressed in vivo, and contains the nominal RCK2 domain. CV562866 affects functional expression of mSlo3 and mSlo1 channels in Xenopus oocytes, decreasing and increasing
expression respectively.

This study examined the hSlo2.2a channel characteristics, which unlike the previously reported rSlo2.2a channel, mediates a non-rectifying K+ current. Bithionol activates hSlo2.2a channels with an EC50 of 1.29±0.12μM and activation was Na+ co-operative. We found a candidate bithionol binding site in the C-terminal domain near the “Cl- bowl”. Due to toxicity of hSlo2.1 expression; determination of the bithionol selectivity of Slo2.χ channels was unattainable. In vivo, Slo2.χ channels act as a background K+ conductance, activated by a variety of conditions, stabilising the resting membrane potential of the cell. This study suggests Slo2.χ are viable pharmacological targets for treatment of inflammatory pain.