Actions of epoxyeicosatrienoic acid on large-conductance Ca2+-activated K+channels in pituitary GH(3) cells

Epoxyeicosatrienoic acids (EETs), a family of cytochrome P450 epoxygenase m etabolites of arachidonic acid, are believed to have an autocrine or paracr ine role in the regulation of neurons or neuroendocrine cells. The effects of 14,15-EET on ionic currents were investigated in rat pituitary GH(3) cel ls. In the whole-cell configuration, 14,15-EET (3 mu M) reversibly increase d the amplitude of the Ca2+-activated K+ current (I-K(Ca)). The 14,15-EET-i nduced increase in I-K(Ca) was unaffected in the presence of 10 mu M thyrot ropin-releasing hormone externally or 10 mu M inositol trisphosphate in the recording pipette. In cells preincubated with pertussis toxin or herbimyci n A, the 14,15-EET-induced increase in I-K(Ca) was also not changed. In the inside-out configuration, 14,15-EET applied intracellularly did not change single-channel conductance, but did increase the opening probability of la rge-conductance Ca2+-activated K+ (BKCa) channels. 14,15-EET (3 mu M) shift ed the activation curve of BK,, channels to less positive membrane potentia l by approximately 15 mV. The change in the kinetic behavior of BKCa channe ls caused by 14,15-EET is explained by a lengthening of open and a shorteni ng of closed times. 14,15-EET increased the activity of BKCa channels in a concentration-dependent manner with an EC50 value of 1 mu M. However, 14,15 -EET did not affect the Ca2+ sensitivity of BKCa channels. The present stud y indicates that 14,15-EET is an opener of BKCa channels in GH(3) cells and that the stimulatory effect of 14,15-EET on these channels may, at least i n part, contribute to the underlying cellular mechanisms by which EETs affe ct neuronal or neuroendocrine function. (C) 2000 Elsevier Science Inc.