Evidence for Dual Activation of IK(M) and IK(Ca) Caused by QO-58 (5-(2,6-Dichloro-5-fluoropyridin-3-yl)-3-phenyl-2-(trifluoromethyl)-1H-pyrazolol[1,5-a]pyrimidin-7-one)

Abstract

QO-58 (5-(2,6-dichloro-5-fluoropyridin-3-yl)-3-phenyl-2-(trifluoromethyl)-1H-pyrazolol[1,5-a]pyrimidin-7-one) has been regarded to be an activator of KV7 channels with analgesic properties. However, whether and how the presence of this compound can result in any modifications of other types of membrane ion channels in native cells are not thoroughly investigated. In this study, we investigated its perturbations on M-type K+ current (IK(M)), Ca2+-activated K+ current (IK(Ca)), large-conductance Ca2+-activated K+ (BKCa) channels, and erg-mediated K+ current (IK(erg)) identified from pituitary tumor (GH3) cells. Addition of QO-58 can increase the amplitude of IK(M) and IK(Ca) in a concentration-dependent fashion, with effective EC50 of 3.1 and 4.2 μM, respectively. This compound could shift the activation curve of IK(M) toward a leftward direction with being void of changes in the gating charge. The strength in voltage-dependent hysteresis (Vhys) of IK(M) evoked by upright triangular ramp pulse (Vramp) was enhanced by adding QO-58. The probabilities of M-type K+ (KM) channels that will be open increased upon the exposure to QO-58, although no modification in single-channel conductance was seen. Furthermore, GH3-cell exposure to QO-58 effectively increased the amplitude of IK(Ca) as well as enhanced the activity of BKCa channels. Under inside-out configuration, QO-58, applied at the cytosolic leaflet of the channel, activated BKCa-channel activity, and its increase could be attenuated by further addition of verruculogen, but not by linopirdine (10 μM). The application of QO-58 could lead to a leftward shift in the activation curve of BKCa channels with neither change in the gating charge nor in single-channel conductance. Moreover, cell exposure of QO-58 (10 μM) resulted in a minor suppression of IK(erg) amplitude in response to membrane hyperpolarization. The docking results also revealed that there are possible interactions of the QO-58 molecule with the KCNQ or KCa1.1 channel. Overall, dual activation of IK(M) and IK(Ca) caused by the presence of QO-58 eventually may have high impacts on the functional activity (e.g., anti-nociceptive effect) residing in electrically excitable cells. Care must be exercised when interpreting data generated with QO-58 as it is not entirely KCNQ/KV7 selective.

Effective Perturbations by Small-Molecule Modulators on Voltage-Dependent Hysteresis of Transmembrane Ionic Currents

“…Mirogabalin (Tarlige ® ) is an orally administered gabapentinoid, and it was thought to be a selective ligand for the α 2 δ-1 subunit of voltage-gated Ca 2+ channels [ 87 ]. More notable than the issue concerning the magnitude of mirogabalin-induced reduction in I Na , is the current observation of the non-linear Hys (V) of I Na(P) elicited by using the upright isosceles-triangular V ramp in pituitary GH 3 lactotrophs [ 88 ]. The presence of mirogabalin in GH 3 cells caused a concentration-dependent inhibition of I Na(T) and I Na(L) amplitude with the estimated IC 50 value of 19.5 and 7.3 μM, respectively [ 88 ].…”

“…More notable than the issue concerning the magnitude of mirogabalin-induced reduction in I Na , is the current observation of the non-linear Hys (V) of I Na(P) elicited by using the upright isosceles-triangular V ramp in pituitary GH 3 lactotrophs [ 88 ]. The presence of mirogabalin in GH 3 cells caused a concentration-dependent inhibition of I Na(T) and I Na(L) amplitude with the estimated IC 50 value of 19.5 and 7.3 μM, respectively [ 88 ]. Moreover, during cell exposure to mirogabalin, the peak I Na(P) activated by the ascending (upsloping) limb of the triangular V ramp became decreased, particularly at the level of −10 mV, while the I Na(P) amplitude at the descending (downsloping) phase was also concurrently reduced at the level of −80 mV.…”

“…As a result, there turned out to be two distinct types of Hys (V) loop; that is, a high-threshold loop with a peak at −10 mV (i.e., activating at a voltage range near the maximal amplitude of transient Na + current ( I Na(T) evoked by brief step depolarization), and a low-threshold loop with a peak at −80 mV (i.e., activating at a voltage near the resting membrane potential). The application of mirogabalin was able to attenuate the Hys (V) strength of I Na(P) effectively [ 88 ]. Under this scenario, the observations reveal that the triangular V ramp -induced I Na(P) undergoes striking Hys (V) behavior with the voltage dependence, and that such Hys (V) loops responding to triangular V ramp are subjected to attenuation by adding mirogabalin.…”

Ion Channels as a Potential Target in Pharmaceutical Designs

“…The ameliorating effect of this compound has been viewed to be closely linked to its activation of KCNQ (K V 7) channels. However, a paper by Wu et al [ 7 ] demonstrated a dual activation of M-type K + ( I K(M) ) and Ca 2+ -activated K + currents ( I K(Ca) ) in GH 3 cells. The presence of QO-58 concentration dependently increased the amplitude of I K(M) and I K(Ca) with the EC 50 values of 3.1 and 4.2 μM, respectively.…”

“…The hysteretic strength of I K(M) activated by a triangular ramp pulse was increased by adding QO-58. Moreover, the QO-58 exposure enhanced the opening probabilities of large-conductance Ca 2+ -activated K + channels as well as shifts in the activation curve of the channel toward a less depolarized potential with no change in the single channel conductance of the channel [ 7 ]. Collectively, the interaction of QO-58 with M-type K + or large-conductance Ca 2+ -activated K + channels to simulate I K(M) or I K(Ca) in excitable cells is expected to occur in a concentration and voltage-dependent manner, assuming that similar in vivo findings occur.…”