Synergistic Inhibition of Delayed Rectifier K+ and Voltage-Gated Na+ Currents by Artemisinin in Pituitary Tumor (GH3) Cells

Abstract

Background: Artemisinin (ART) is an anti-malarial agent reported to influence endocrine function. Methods: Effects of ART on ionic currents and action potentials (APs) in pituitary tumor (GH₃) cells were evaluated by patch clamp techniques. Results: ART inhibited the amplitude of delayed-rectifier K⁺ current (I_K(DR)) in response to membrane depolarization and accelerated the process of current inactivation. It exerted an inhibitory effect on I_K(DR) with an IC₅₀ value of 11.2 µM and enhanced I_K(DR) inactivation with a K_D value of 14.7 µM. The steady-state inactivation curve of I_K(DR) was shifted to hyperpolarization by 10 mV. Pretreatment of chlorotoxin (1 µM) or iloprost (100 nM) did not alter the magnitude of ART-induced inhibition of I_K(DR) in GH₃ cells. ART also decreased the peak amplitude of voltage-gated Na⁺ current (I_Na) with a concentration-dependent slowing in inactivation rate. Application of KMUP-1, an inhibitor of late I_Na, was effective at reversing ART-induced prolongation in inactivation time constant of I_Na. Under current-clamp recordings, ART alone reduced the amplitude of APs and prolonged the duration of APs. Conclusion: Under ART exposure, the inhibitory actions on both I_K(DR) and I_Na could be a potential mechanisms through which this drug influences membrane excitability of endocrine or neuroendocrine cells appearing in vivo.

Evidence for Effective Multiple K+-Current Inhibitions by Tolvaptan, a Non-peptide Antagonist of Vasopressin V2 Receptor

“…Once whole-cell mode was established, the examined cells were held at−50 mV, and the depolarizing pulse to +50 mV with a duration of 1 s was then delivered to them. Consistent with previous observations (Wang et al, 2008; So et al, 2017), the I K(DR) in response to such pulse protocol was drastically evoked in these cells. Unexpectedly, as cells were exposed to different concentrations of TLV, the I K(DR) elicited by membrane depolarization in these cells was progressively decreased (Figure 1A).…”

“…GH 3 , a clonal cell line derived from a rat prolactin-secreting pituitary tumor, was obtained from the Bioresources Collection and Research Center (BCRC-60015; Hsinchu, Taiwan). Cells were routinely cultured in Ham's F-12 medium supplemented with 15% heat-inactivated horse serum (v/v), 2.5% fetal calf serum (v/v), and 2 mM L-glutamine (Liu et al, 2009; So et al, 2017, 2018). In another separate set of experiments, we treated GH 3 cells with vasopressin (1 μM) at 37°C for 6 h. The MDCK cell line (BCRC-60004), a canine renal tubular cell line, was also obtained from the Bioresource Collection and Research Center (Hsinchu, Taiwan).…”

“…The electrodes used during the recordings had a tip resistance of 3–5 MΩ when filled with different internal solution described above. Ion currents were measured in either whole-cell, cell-attached or inside-out configuration of a standard patch-clamp technique with an RK-400 (Bio-Logic, Claix, France) or an Axopatch-200B (Molecular Devices, Sunnyvale, CA) amplifier (So et al, 2017; Wu et al, 2017b). Changes in membrane potential were measured under current-clamp configuration.…”

“…These properties can be expected to limit the Na + channel, thereby leading to depolarization block and accommodation of repetitive firing at high frequencies (Rudy and McBain, 2001; Tateno and Robinson, 2007). K V channels from the K V 3.1-K V 3.2 types are the major determinants of I K(DR) in pituitary GH 3 cells (Wang et al, 2008; So et al, 2017). However, whether TLV, expected to be a non-peptide vasopressin antagonist, exerts any perturbations on these types of K + currents (e.g., I K(M) and I K(DR) ) or on membrane potential remains largely unexplored, although a previous report showed the ability of TLV to suppress the store-operated Ca 2+ entry through an interaction with the Orail1 protein (Rahman and Rahman, 2017) and to increase cytosolic Ca 2+ in Madin-Darby canine kidney (MDCK) cells (Tamma et al, 2017).…”

Antiarrhythmic Effect of Artemisinin in an Ex-vivo Model of Brugada Syndrome Induced by NS5806

“…In addition to its antimalarial effect, its antiarrhythmic effect, which includes suppression of the I K1 , I to , and I Ks channels, was reported previously. 7) 8) 9) 10) Therefore, we evaluated the hypothesis that inhibition of I to channels by artemisinin may play a role in the suppression of ventricular arrhythmia in canine wedge preparation models of BrS.…”