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

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 GH(3) cells. Hyperpolarization-elicited K+ currents in GH(3) 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 (I (K(erg))). Addition of DEHP to GH(3) cells suppressed the amplitude of I (K(erg)) in a concentration-dependent manner with an IC50 value of 16.3 mu M. With a two-pulse protocol, addition of DEHP shifted the activation curve of I (K(erg)) to a depolarized potential by approximately 10 mV with no change in the rate of I (K(erg)) deactivation. This compound did not have any effects on delayed rectifier K+ current in GH(3) cells, while 4-aminopyridine-3-methanol (100 mu M) suppressed this current significantly. DBEP (30 mu M) had little or no effect on I (K(erg)), while DMGP (30 mu M) slightly reduced it. In inside-out configuration, DEHP (30 mu M) applied to the bath slightly reduced the activity of large-conductance Ca2+-activated K+ channels. DEHP (30 mu M) 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 GH(3) 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.