Nongenomic inhibition of catecholamine secretion by 17β-estradiol in PC12 cells

We investigated the effects of 17 beta-estradiol, an estrogen, on [H-3]norepinephrine ([H-3]NE) secretion in PC12 cells. Pretreatment with 17 beta-estradiol reduced 70 mM K+-induced [H-3]NE secretion in a concentrationdependent manner with a half-maximal inhibitory concentration (IC50) of 2 +/- 1 mu M. The 70 mM K+-induced cytosolic free Ca2+ concentration ([Ca2+](i)) rise was also reduced when the cells were treated with 17 beta-estradiol (IC50 = 15 +/- 2 mu M). Studies with voltage-sensitive calcium channel (VSCC) antagonists such as nifedipine and omega-conotoxin GVIA revealed that both L- and N-type VSCCs were affected by 17 beta-estradiol treatment. The 17 beta-estradiol effect was not changed by pretreatment of the cells with actinomycin D and cycloheximide for 5 h. In addition, treatment with pertussis or cholera toxin did not affect the inhibitory effect of 17 beta-estradiol. 17 beta-Estradiol also inhibited the ATP-induced [H-3]NE secretion and [Ca2+](i) rise. In PC12 cells, the ATP-induced [Ca2+](i) rise is known to occur through P2X(2) receptors, the P2Y(2)-mediated phospholipase C (PLC) pathway, and VSCCs. 17 beta-Estradiol pretreatment during complete inhibition of the PLC pathway and VSCCs inhibited the ATP-induced [Ca2+](i) rise. Our results suggest that 17 beta-estradiol inhibits catecholamine secretion by inhibiting L- and N-type Ca2+ channels and P2X(2) receptors in a nongenomic manner.