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 (IK(DR)) in response to membrane depolarization and accelerated the process of current inactivation. It exerted an inhibitory effect on IK(DR) with an IC50 value of 11.2 µM and enhanced IK(DR) inactivation with a KD value of 14.7 µM. The steady-state inactivation curve of IK(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 IK(DR) in GH3 cells. ART also decreased the peak amplitude of voltage-gated Na+ current (INa) with a concentration-dependent slowing in inactivation rate. Application of KMUP-1, an inhibitor of late INa, was effective at reversing ART-induced prolongation in inactivation time constant of INa. 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 IK(DR) and INa could be a potential mechanisms through which this drug influences membrane excitability of endocrine or neuroendocrine cells appearing in vivo.

Keywords: Action potential; Artemisinin; Current kinetics; Delayed-rectifier K+ current; Pituitary cell; Voltage-gated Na+ current.