Estrogen-induced downregulation of TASK-1 expression through estrogen receptor ß in N2A cells.

BACKGROUND: Our previous data revealed that reduction of TASK-1 expression, as a consequence of exposure to 17ß-estradiol, could participate in neuroprotective effects in N2A cells. However, it is unclear which estrogen receptor underlies these effects of 17ß-estradiol. METHODS AND RESULTS: In this study, the knockdown experiments are carried out to clarify the estrogen receptor responsible for effects of estrogen on TASK-1 channels. Subsequently, data from QPCR measurements reveal that estrogen receptor ß (ERß), but not estrogen receptor α, serves as a binding target for 17ß-estradiol after a 48-h treatment. CONCLUSIONS: The current result suggests the implication of the ERß-dependent manner in the pro-proliferative action of estrogen via TASK-1 channels.

The inhibitory effects of nifedipine on outward voltage-gated potassium currents in mouse neuroblastoma N2A cells.

BACKGROUND: Voltage-gated K(+) (Kv) channels have a pivotal role in tuning the action potential duration and excitability in neuronal cells. Although Ca(2+) channel antagonist nifedipine exhibited an inhibitory effect on cardiac Kv currents, a possible action of nifedipine on neuronal Kv currents has not been fully investigated. METHODS: The effects of nifedipine on elicited Kv currents were characterized using whole-cell recording in mouse neuroblastoma N2A cells. RESULTS: Exposure to nifedipine induced a dose-dependent inhibition of Kv currents with an IC50 value of 22.3±4.2µM and prolonged the time course of activation. The half-maximum activation potential was 1.6±1.7mV in control conditions and became 13.5±1.5mV in 50µM nifedipine. In addition, the decay rate of Kv currents was substantially accelerated by 39.5% at +60mV. For the voltage-dependent inactivation, the half-maximum inactivation potential was -13.8±0.8mV and strongly shifted to the left following treatment with 50µM nifedipine. CONCLUSION: Treatment with nifedipine exerted a strong influence on the activation and inactivation rate of Kv currents as well as an obvious leftward shift in the inactivation curve. These data indicated that nifedipine exerted an inhibitory effect on Kv currents in N2A cells.

17ß-Estradiol Upregulated Expression of α and ß Subunits of Larger-Conductance Calcium-Activated K(+) Channels (BK) via Estrogen Receptor ß.

Large-conductance Ca(2+)-activated K(+) channels, which were known as BK channels, were widely distributed in brain tissues and played a crucial role in neuroprotection. Previous studies found that estrogen, a steroid hormone, was able to interact with distinct K(+) channels such as Kv (voltage-gated K(+) channels) in various tissues. However, current knowledge about possible effects of estrogen on BK channels is rather poor. In the present study here, the investigation for the interaction of estrogen with BK channels was performed in mouse N2A cells and human SK-N-SH cells. At first, the different expression patterns of α and ß subunits of BK channels in these cells were explored by conducting RT-PCR. After exposure to varying dose of 17ß-estradiol (E2) for 24 h, the messenger RNA (mRNA) levels of these BK channel subunits in both N2A and SK-N-SH cells were significantly increased in a concentration-dependent way. A prolonged incubation for 48 h also potentiated the effects of E2 on ß1 and ß4 subunits in N2A cells as well as α and ß3 subunits in SK-N-SH cells. The small interfering RNAs (siRNAs) against the ERα (siERα) or ERß (siERß) was induced into N2A and SK-N-SH cells by transfection and resulted in a decrease in the level of corresponding ER transcript. Furthermore, treatment with siERß but not siERα attenuated the action of E2 on BK channel subunits, suggesting that estradiol exerted its action by binding to ERß. Our data indicated that 17ß-estradiol was able to regulate the expression of BK channel subunits via ERß.

The Inhibitory Effects of Ca2+ Channel Blocker Nifedipine on Rat Kv2.1 Potassium Channels.

It is well documented that nifedipine, a commonly used dihydropyridine Ca2+ channel blocker, has also significant interactions with voltage-gated K+ (Kv) channels. But to date, little is known whether nifedipine exerted an action on Kv2.1 channels, a member of the Shab subfamily with slow inactivation. In the present study, we explored the effects of nifedipine on rat Kv2.1 channels expressed in HEK293 cells. Data from whole-cell recording showed that nifedipine substantially reduced Kv2.1 currents with the IC50 value of 37.5 ± 5.7 µM and delayed the time course of activation without effects on the activation curve. Moreover, this drug also significantly shortened the duration of inactivation and deactivation of Kv2.1 currents in a voltage-dependent manner. Interestingly, the half-maximum inactivation potential (V1/2) of Kv2.1 currents was -11.4 ± 0.9 mV in control and became -38.5 ± 0.4 mV after application of 50 µM nifedipine. The large hyperpolarizing shift (27 mV) of the inactivation curve has not been reported previously and may result in more inactivation for outward delayed rectifier K+ currents mediated by Kv2.1 channels at repolarization phases. The Y380R mutant significantly increased the binding affinity of nifedipine to Kv2.1 channels, suggesting an interaction of nifedipine with the outer mouth region of this channel. The data present here will be helpful to understand the diverse effects exerted by nifedipine on various Kv channels.