Hydrophobic Interactions as Key Determinants to the KCa3.1 Channel Closed Configuration

Negative Gating Modulation by (R)-N-(Benzimidazol-2-yl)-1,2,3,4-tetrahydro-1-naphthylamine (NS8593) Depends on Residues in the Inner Pore Vestibule: Pharmacological Evidence of Deep-Pore Gating of KCa2 Channels

“…At the present time we therefore favor the hypothesis, that the diverse positive/negative modulator pharmacology directly reflects the complexity and extended participation of even remotely positioned parts of K Ca 2 (and accessory proteins) in the gating process. Cysteine scanning experiments have clearly shown that the gate of both K Ca 2 and K Ca 3 channels is positioned very close to or even encompasses the quite outwardly displaced K ϩ selectivity filter (Bruening-Wright et al, 2002Klein et al, 2007;Garneau et al, 2009), a finding that has to be reconciled with the primary Ca 2ϩ -binding event occurring on CaM at the cytoplasmic C terminus. We think of K Ca 2 (and K Ca 3) channel gating as a series of events comprising Ca 2ϩ -binding, CaM/CaMBD/C-terminal conformational change, leading to a transduction via S6 (possibly involving S5 stabilization) to deep-pore gating structures and eventual opening of the channel.…”

“…The energy of the ensuing conformational change is transferred to the transmembrane (TM) regions to open the gate. Unlike K v channels, which are gated by a rotational constriction of the intracellular aperture formed by the lower part of the four S6 TM helixes, the physical gates of K Ca 2 and K Ca 3.1 channels seem to be deeply buried in the inner pore vestibule, close to or even overlapping with the K ϩ selectivity filter (Bruening-Wright et al, 2002Klein et al, 2007;Garneau et al, 2009).…”

New Positive Ca2+-Activated K+ Channel Gating Modulators with Selectivity for KCa3.1

“…Since none of the benzothiazole-type K Ca 2/3 activators, including SKA-31, SKA-111, SKA-121, and their many derivatives, had ever increased K Ca 3.1 or K Ca 2 currents in our hands at Ca 21 concentrations lower than 100 nM or in the absence of Ca 21 with KF-based pipette solutions, we do not ascribe this effect to a direct channel opening component in their mechanism of action, like that reported for GW542573X and (-)-CM-TMPF for K Ca 2.1 (Hougaard et al, 2009. Unlike SKA-121, which we think is binding at the CaM/CaMBD interface, (-)CM-TMPF has been found to interact with positions deep within the inner pore vestibule close to the selectivity filter, where the gate of K Ca 2/3 channels seems to be located (Bruening-Wright et al, 2002Garneau et al, 2009;Klein et al, 2007). It therefore seems reasonable to attribute the Ca 21 -independent K Ca 2.1 channel activation by (-)-CM-TMPF to a directly opening effect on the gate and use this explanation to account for the fact that (-)-CM-TMPF increases K Ca 2.1 currents to roughly 40% of their maximal activity at Ca 21 concentrations between 10 and 100 nM and then levels off in its opening/activating activity at higher Ca 21 concentrations .…”

Selective Activation of the SK1 Subtype of Human Small-Conductance Ca2+-Activated K+ Channels by 4-(2-Methoxyphenylcarbamoyloxymethyl)-piperidine-1-carboxylic Acid tert-Butyl Ester (GW542573X) Is Dependent on Serine 293 in the S5 Segment

“…On the other hand Ba 2ϩ , a K ϩ analog that specifically binds at the selectivity filter and blocks the current of K ϩ through SK channels only in the open state, prevents MTSEA ϩ modification at Ala384, indicating that the gate and the selectivity filter may be functionally connected. A similar experimental strategy was also adopted for the IK channel (Klein et al, 2007;Garneau et al, 2009), clearly revealing that Val275, which is equivalent to Ala384 in SK2, is accessible in the closed state for reduction by Ag ϩ , a K ϩ -sized ion. It is noteworthy that this study also showed that mutations at specific hydrophobic amino acids (A279G, V282G in IK, and V391G in SK2) in the pore region lead to constitutively active channels being insensitive toward [Ca 2ϩ ] i .…”