Effective Activation of BKCa Channels by QO-40 (5-(Chloromethyl)-3-(Naphthalen-1-yl)-2-(Trifluoromethyl)Pyrazolo [1,5-a]pyrimidin-7(4H)-one), Known to Be an Opener of KCNQ2/Q3 Channels.

Wei-Ting Chang,Sheng-Nan Wu

doi:10.3390/ph14050388

Abstract

QO-40 (5-(chloromethyl)-3-(naphthalene-1-yl)-2-(trifluoromethyl) pyrazolo[1,5-a]pyrimidin-7(4H)-one) is a novel and selective activator of KCNQ2/KCNQ3 K+ channels. However, it remains largely unknown whether this compound can modify any other type of plasmalemmal ionic channel. The effects of QO-40 on ion channels in pituitary GH3 lactotrophs were investigated in this study. QO-40 stimulated Ca2+-activated K+ current (IK(Ca)) with an EC50 value of 2.3 μM in these cells. QO-40-stimulated IK(Ca) was attenuated by the further addition of GAL-021 or paxilline but not by linopirdine or TRAM-34. In inside-out mode, this compound added to the intracellular leaflet of the detached patches stimulated large-conductance Ca2+-activated K+ (BKCa) channels with no change in single-channel conductance; however, there was a decrease in the slow component of the mean closed time of BKCa channels. The KD value required for the QO-40-mediated decrease in the slow component at the mean closure time was 1.96 μM. This compound shifted the steady-state activation curve of BKCa channels to a less positive voltage and decreased the gating charge of the channel. The application of QO-40 also increased the hysteretic strength of BKCa channels elicited by a long-lasting isosceles-triangular ramp voltage. In HEK293T cells expressing α-hSlo, QO-40 stimulated BKCa channel activity. Overall, these findings demonstrate that QO-40 can interact directly with the BKCa channel to increase the amplitude of IK(Ca) in GH3 cells.

Highlights

QO-40 (5-(chloromethyl)-3-(naphthalene-1-yl)-2-(trifluoromethyl)pyrazolo[1,5-a]pyrimidin7-(4H)-one) is a highly pure, synthetic, and biologically active compound (Figure 1)
In the firstofstage of electrophysiological measurements, we performed the whole-cell configuration the patch-clamp experiments to evaluate any possible adjustments of configuration of the to evaluate anyidentified possible from adjustments of QO-40, a synthetic andpatch-clamp biologicallyexperiments active compound, on IK(Ca)
QO-40 could result in evident decrease in pthe chanHerein, the results showed that the presence of QO-40 could in opening an evident decrease nel closure time, notwithstanding its ineffectiveness on theresult mean time of the in the channel closure time, notwithstanding its ineffectiveness on the mean opening channel observed at +60 mV

Summary

Introduction

QO-40 (5-(chloromethyl)-3-(naphthalene-1-yl)-2-(trifluoromethyl)pyrazolo[1,5-a]pyrimidin7-(4H)-one) is a highly pure, synthetic, and biologically active compound (Figure 1). This compound has been previously reported to enhance KCNQ2/KCNQ3 heteromeric currents expressed in Xenopus oocytes [1]. QO58-lysine, a compound structurally similar to QO-40, can activate neuronal KCNQ channels and exert antinociceptive effects on inflammatory pain [2,3,4,5,6]. The QO-58-induced amelioration of inflammatory pain observed in rodents was previously viewed as being accompanied by the activation of KCNQ-encoded. None of the studies have thoroughly investigated with the underlying mechanism of action of QO-40 or its structurally similar compounds on other types of ionic currents (e.g., Ca2+ -activated K+ current, [IK(Ca) ]).

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