High Efficacy by GAL-021: A Known Intravenous Peripheral Chemoreceptor Modulator that Suppresses BK(Ca)-Channel Activity and Inhibits I(K(M)) or I(h)

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 Ca(2+)-activated K(+) (BK(Ca)) channels has been reported. In pituitary tumor (GH(3)) cells, we found that the presence of GAL-021 decreased the amplitude of macroscopic Ca(2+)-activated K(+) current (I(K(Ca))) in a concentration-dependent manner with an effective IC(50) of 2.33 μM. GAL-021-mediated reduction of I(K(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 BK(Ca) channels. This agent also resulted in a rightward shift in voltage dependence of the activation curve of BK(Ca) 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 BK(Ca) 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 IC(50) 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 BK(Ca)-channel open probabilities, and GAL-021-mediated suppression of BK(Ca)-channel activity was attenuated by further addition of BMS-191011. Collectively, the GAL-021 effects presented herein do not exclusively act on BK(Ca) channels and these modifications on ionic currents exert significant influence on the functional activities of electrically excitable cells occurring in vivo.