The inhibition by di(2-ethylhexyl)-phthalate of erg-mediated K+ current in pituitary tumor (GH3) cells

Abstract

DEHP (bis(2-ethylhexyl)-phthalate) known to be an endocrine-disrupting chemical is a widely used phthalate. Little information regarding the effects of phthalate esters on ion currents is available. In this study, the effects of DEHP and other phthalate esters (DBEP: di(2-butoxyethyl)-phthalate and DMGP: di(2-methylglycol)-phthalate) on ion currents were investigated in pituitary GH₃ cells. Hyperpolarization-elicited K⁺ currents in GH3 cells bathed in high-K⁺, Ca²⁺-free solution were examined to evaluate the effects of DEHP, DBEP, and DMGP on the ether-a`-go-go-related-gene (erg) K⁺ current (IK(erg)). Addition of DEHP to GH₃ cells suppressed the amplitude of IK(erg) in a concentration-dependent manner with an IC₅₀ value of 16.3 μM. With a two-pulse protocol, addition of DEHP shifted the activation curve of IK(erg) to a depolarized potential by approximately 10 mV with no change in the rate of IK(erg) deactivation. This compound did not have any effects on delayed rectifier K⁺ current in GH₃ cells, while 4-aminopyridine-3-methanol (100 μM) suppressed this current significantly. DBEP (30 μM) had little or no effect on IK(erg), while DMGP (30 μM) slightly reduced it. In inside-out configuration, DEHP (30 μM) applied to the bath slightly reduced the activity of large-conductance Ca²⁺-activated K⁺ channels. DEHP (30 μM) increased the frequency of spontaneous action potentials (APs); however, this compound at the same concentration had no effect on AP firing in KCNH2 siRNA-transfected GH₃ cells. The effects described herein can contribute to their actions on functional activity of endocrine or neuroendocrine cells if similar results are found in vivo.

Stimulation of electroporation‐induced inward currents in glioblastoma cell lines by the heat shock protein inhibitor AUY922

“…The amplitude of I K(Ca) was affected by verruculogen, but not apamin, suggesting that the activity of BK Ca channels arose primarily from the activation of I K(Ca) caused by a large hyperpolarization. 19,22,23 Single-channel recordings in U373 and U87 cells clearly showed that the activity of BK Ca channels was blocked by verruculogen (data not shown). Findings from the present study could be explained by the fact that AUY is able to increase the amplitude of I MEP and intracellular Ca 2+ , thereby leading to an elevation of BK Ca channel activity in glioblastoma cells.…”

“…Our results demonstrate that the amplitude of I K(Ca) is readily increased in U373 cells by an increase in intracellular Ca 2+ concentration due to activation of I MEP . The amplitude of I K(Ca) was affected by verruculogen, but not apamin, suggesting that the activity of BK Ca channels arose primarily from the activation of I K(Ca) caused by a large hyperpolarization . Single‐channel recordings in U373 and U87 cells clearly showed that the activity of BK Ca channels was blocked by verruculogen (data not shown).…”

“…6a). In addition, 1 lmol/L verruculogen, a potent inhibitor of BK Ca channels, 23 produced a profound reduction in AUY-stimulated I K(Ca) in U373 cells (Fig. 6b).…”

Characterization of Convergent Suppression by UCL-2077 (3-(Triphenylmethylaminomethyl)pyridine), Known to Inhibit Slow Afterhyperpolarization, of erg-Mediated Potassium Currents and Intermediate-Conductance Calcium-Activated Potassium Channels

“…These currents inherently existing in neurons or in different types of electrically excitable cell, such as endocrine or neuroendocrine cells, can highly influence the maintenance of the resting potential as well as the increase in subthreshold excitability [11,12], thereby leading to marked changes in the discharge rate of spontaneous action potentials (APs) [13][14][15][16]. As a consequence, the resultant perturbations in the activity of such K + channels have the propensity to change the stimulus-secretion coupling of these cells [13,[17][18][19]. Previous work has also revealed that the activity of K erg channels can be a regulator of tumor cell apoptosis and proliferation [20].…”

Effectiveness of nalbuphine, a κ‐opioid receptor agonist and μ‐opioid receptor antagonist, in the inhibition of INa, IK(M), and IK(erg) unlinked to interaction with opioid receptors

“…We next studied the possible effects of NAL on I K(erg) in these cells. Similar to the voltage protocol used for the measurements of I K(M) (Huang et al, ; Wu, Yang, Yeh, & Huang, ), we bathed cells in high‐K + , Ca 2+ ‐free solution, and the pipette used was filled with K + ‐containing solution. As the cell was maintained at −10 mV, I K(erg) was elicited by membrane hyperpolarization to −80 mV (Figure A).…”