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 K_Ca2 Channels

Abstract

Acting as a negative gating modulator, (R)-N-(benzimidazol-2-yl)-1,2,3,4-tetrahydro-1-naphthylamine (NS8593) shifts the apparent Ca 2ϩ

Physiologie, pharmacologie et modélisation de canaux potassiques

“…L'EBIO agit au niveau de l'extrémité carboxy-terminale du domaine cytoplasmique qui est associée physiquement à la calmoduline, une protéine jouant le rôle de senseur de Ca 2+ [37]. En ce qui concerne le modulateur négatif NS8593, il a été en revanche démontré qu'il agissait dans la cavité située en dessous du filtre de sélectivité (Figure 2) [38]. Quant au composé Ohmline, son site d'action se localiserait à l'interface des canaux et de la membrane cellulaire [35,39].…”

Pharmacological gating modulation of small- and intermediate-conductance Ca2+-activated K+channels (KCa2.x and KCa3.1)

“…1). 76 Since the physical gate of KCNN channels has -by independent measures -been located at a "deep" position in the channel, 77 we speculate that the mechanism behind the negative gating modulation of NS8593, may be due to its interaction with the gate itself. A crystal with bound NS8593 would be very interesting!…”

“…78 However, the inhibition by TRAM-34 shows no clear dependence on intracellular Ca 2C (or degree of activation) and the effect cannot be "reversed" by positive modulators. 76 In contrast to NS8593, Bu-TPMF, the K Ca 2.1 selective negative gating modulator, interacts with a site lower down in the inner pore vestibule in TM5 (Fig. 1).…”

“…In practical terms, if NS8593 is applied at a relatively low Ca 2C concentration (low degree of channel activation) the inhibitor potency appears high, while it is essentially without effect at higher Ca 2C concentrations (high degree of channel activation). 70,76 The distinction between the Ca 2C concentration per se and the degree of activation is essential here, since the effect of NS8593 also disappear at a high degree of channel activation obtained by a combination of a low Ca 2C -concentration and a positive modulator like NS309 or SKA-31. 45,70,76 Site(s) of action In contrast to small molecule blockers, NS8593 does not displace apamin in binding studies, and the compound remains active on a channel made apamin-insensitive by specific mutations in the outer pore mouth.…”

“…70,76 The distinction between the Ca 2C concentration per se and the degree of activation is essential here, since the effect of NS8593 also disappear at a high degree of channel activation obtained by a combination of a low Ca 2C -concentration and a positive modulator like NS309 or SKA-31. 45,70,76 Site(s) of action In contrast to small molecule blockers, NS8593 does not displace apamin in binding studies, and the compound remains active on a channel made apamin-insensitive by specific mutations in the outer pore mouth. 71 Another difference is that NS8593 is able to reach its binding site both when applied from the outside and from the inside of the membrane.…”