High Efficacy by GAL-021: A Known Intravenous Peripheral Chemoreceptor Modulator that Suppresses BKCa-Channel Activity and Inhibits IK(M) or Ih

Abstract

GAL-021 has recently been developed as a novel breathing control modulator. However, modifications of ionic currents produced by this agent remain uncertain, although its efficacy in suppressing the activity of big-conductance Ca2+-activated K+ (BKCa) channels has been reported. In pituitary tumor (GH3) cells, we found that the presence of GAL-021 decreased the amplitude of macroscopic Ca2+-activated K+ current (IK(Ca)) in a concentration-dependent manner with an effective IC50 of 2.33 μM. GAL-021-mediated reduction of IK(Ca) was reversed by subsequent application of verteporfin or ionomycin; however, it was not by that of diazoxide. In inside-out current recordings, the addition of GAL-021 to the bath markedly decreased the open-state probability of BKCa channels. This agent also resulted in a rightward shift in voltage dependence of the activation curve of BKCa channels; however, neither the gating charge of the curve nor single-channel conductance of the channel was changed. There was an evident lengthening of the mean closed time of BKCa channels in the presence of GAL-021, with no change in mean open time. The GAL-021 addition also suppressed M-type K+ current with an effective IC50 of 3.75 μM; however, its presence did not alter the amplitude of erg-mediated K+ current, or mildly suppressed delayed-rectifier K+ current. GAL-021 at a concentration of 30 μM could also suppress hyperpolarization-activated cationic current. In HEK293T cells expressing α-hSlo, the addition of GAL-021 was also able to suppress the BKCa-channel open probabilities, and GAL-021-mediated suppression of BKCa-channel activity was attenuated by further addition of BMS-191011. Collectively, the GAL-021 effects presented herein do not exclusively act on BKCa channels and these modifications on ionic currents exert significant influence on the functional activities of electrically excitable cells occurring in vivo.

The Integrated Effects of Brivaracetam, a Selective Analog of Levetiracetam, on Ionic Currents and Neuronal Excitability

“…As depicted in Figure 3 A, the 2 s long hyperpolarizing command voltages ranging from −40 to −120 mV could readily evoke an inward current with slowly activating and deactivating time courses in response to such sustained hyperpolarization. This type of ionic current has been previously identified to be I h [ 49 , 63 , 64 ]. When the cells were exposed to BRV (3 µM), the I h amplitude was unaffected.…”

“…Alternatively, in the continued presence of BRV, the subsequent addition of GAL-021 or PF1022A reversed the BRV-mediated decrease in BK Ca -channel activity; however, further application of TRAM39 failed to exert any effects ( Figure 6 B). TRAM39 was previously reported to be an inhibitor of intermediate-conductance Ca 2+ -activated K + channels [ 66 ], whereas GAL-021 or PF1022A alone was shown to effectively suppress BK Ca -channel activity [ 64 , 67 ].…”

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

“…We next tested whether the stimulatory effect of QO-40 on I K(Ca) was attenuated by linopirdine, TRAM-34, GAL-021, or paxilline. Linopirdine inhibits M-type K + current ( I K(M) ), and TRAM-34 inhibits intermediate-conductance Ca 2+ -activated K + (IK Ca ) channels [ 15 , 22 , 23 ], while GAL-021 and paxilline suppress the activity of large-conductance Ca 2+ -activated K + (BK Ca ) channels [ 21 , 24 , 25 ]. As demonstrated in Figure 3 , when cells were continually exposed to QO-40 (3 μM), neither linopirdine (10 μM) nor TRAM-34 (3 μM) could attenuate QO-40-stimulated I K(Ca) ; conversely, the subsequent addition of GAL-021 (3 μM) or paxilline (1 μM) led to effective attenuation of the increase in I K(Ca) amplitude.…”

Modulating Hyperpolarization-Activated Cation Currents through Small Molecule Perturbations: Magnitude and Gating Control

“…Furthermore, cilobradine was able to suppress delayed-rectifier K + currents ( I K(DR) ) along with an increase in the inactivation time course of the current. As the cilobradine concentration increased from 1 to 3 μM, the midpoint of the steady-state inactivation curve of I K(DR) was shifted along the voltage axis towards hyperpolarizing voltage by approximately 7 mV with no change in the gating charge of the curve during exposure to 1 or 3 μM cilobradine [ 30 ]. It is also important to note that exposure to cilobradine has been previously reported to modulate balance function, given that it may concertedly influence functional HCN channels in vestibular hair cells of the inner ear [ 47 ] and the K V 3.1 channels, which are enriched in the auditory pathway [ 48 ].…”