Estrogen modulates potassium currents and expression of the Kv4.2 subunit in GT1-7 cells

The proper maintenance of reproduction requires the pulsatile secretion of gonadotropin-releasing hormone (GnRH), which is ensured by synchronized periodic firing of multiple GnRH neurons. Both hormone secretion and electrophysiological properties of GnRH cells are influenced by estrogen. The impact of 17beta-estradiol treatment on the function of voltage gated A- and K-type potassium channels, known modulators of firing rate, was therefore examined in our experiments using immortalized GnRH-producing GT1-7 neurons. Whole cell patch clamp recordings showed the absence of the A-type current in GT1-7 cells cultured in estrogen-free medium and after 8h 17beta-estradiol treatment. Exposure of the cells to 17beta-estradiol for 24 and 48 h, respectively, resulted in the appearance of the A-type current. The induction of the A-type current by 17beta-estradiol was dose-related (50 pM to 15 nM range). In contrast, the K-type potassium current was apparent in the estrogen-free environment and 17beta-estradiol administration significantly decreased its amplitude. Co-administration of 17beta-estradiol and estrogen receptor blocker, Faslodex (ICI 182,780; 1 microM) abolished the occurrence of the A-type current. Real-time PCR data demonstrated that expression of the Kv4.2 subunit of the A-type channel was low at 0, 0.5, 2 and 8h, peaked at 24h and diminished at 48 h 17beta-estradiol treatment (15 nM). These data indicate that potassium channels of GT1-7 neurons are regulated by estrogen a mechanism that might contribute to modulation of firing rate and hormone secretion in GnRH neurons.