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

Te-Ling Lu,Zi-Han Gao,Shih-Wei Li,Sheng-Nan Wu

doi:10.3390/biom10020188

Te-Ling Lu, Zi-Han Gao + Show 2 more

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https://doi.org/10.3390/biom10020188

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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.

Highlights

GAL-021 has recently been developed as a novel breathing control modulator thought to preserve respiratory drive and to protect patients from the respiratory impairment resulting from opioids and other modalities; it notably did not influence analgesia [1,2,3,4,5,6,7]
As whole-cell model, that is, when membrane patch was broken by suction, was achieved, we maintained the examined cell at the level of 0 mV, a level which was delivered to inactivate other types of outwardly rectifying K+ currents [36], and ionic currents were evoked by a series of voltage pulses ranging between 0 and +80 mV
The principal findings of this study are as follows: First, in pituitary GH3 lactotrophs, the presence of GAL-021 directly inhibits depolarization-elicited IK(Ca) amplitude in a concentration-dependent manner; second, the inhibitory effect of GAL-021 on the open-state probability of BKCa channels occurs in a voltage-dependent manner; third, there is a lengthening in mean closed time of these channels in its presence, albeit no change in mean open time of the channel; fourth, GAL-021 has minimal noticeable effect on IK(erg) amplitude, it mildly suppresses IK(M); fifth, GAL-021 at a concentration greater than 30 μM suppressed the amplitude of Ih; and sixth, GAL-021 suppresses the probabilities of BKCa-channel openings in α-hSlo-expressing HEK-293T cells

Summary

Introduction

GAL-021 has recently been developed as a novel breathing control modulator thought to preserve respiratory drive and to protect patients from the respiratory impairment resulting from opioids and other modalities; it notably did not influence analgesia [1,2,3,4,5,6,7]. The big-conductance Ca2+-activated K+ (BKCa) channels (KCa1.1, KCNMA1, Slo1), belonging to family of voltage-activated K+ channels, are stimulated by increasing Ca2+ concentrations in the cell and by membrane depolarization, and the channel activation of their own accord can conduct large amounts of potassium ions (K+) across the cell membrane. BKCa channels, which are functionally expressed in a variety of cells, can play substantial roles in physiological and pathophysiological events including neurotransmitter release, muscle relaxation, and oxygen sensing in chemoreceptor cells [1,8,10,11,12,13,14,15,16,17,18,19]. It is noted that BMS-204352 (MaxiPostTM), an activator of BKCa channels, could activate a voltage-independent KCNQ4-encoded current [20,21]

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