Androgens block outward potassium currents and decrease spontaneous action potentials in GH3 cells

Abstract

Androgens produce nongenomic effects in several cells by different mechanisms, including ion channel modulation. Adenohypophyseal cells express several K(+) channels, including voltage and Ca(2+)-dependent K(+) (BK) channels, which might be the target of androgens to modulate cellular action potentials and hormonal secretion. Androgen effects were studied in GH3 cells (from anterior pituitary rat tumor) by means of the patch-clamp technique. Cells were continuously perfused with saline solution, in the absence or presence of the androgens studied, while applying 40 mV pulses of 400 ms from a holding potential of -60 mV in whole-cell configuration with nystatin-perforated patches. Androgens reversibly blocked noninactivating K(+) currents in a concentration-dependent manner without a latency period and with an order of efficacy of: 5β-dihydrotestosterone (DHT)>testosterone>5α-DHT. RT-PCR showed two isoforms of the α-pore forming subunits of BK channels. These channels are responsible for one third of the noninactivating current, according to the blockade of paxilline, a selective BK antagonist. Androgens seem to directly interact with BK channels since they were blocked in excised inside-out patches and independent of the whole-cell configuration and the NO-cGMP-dependent pathway. Testosterone, but not 5α- or 5β-DHT, increased BK currents in HEK-293 cells overexpressing the short isoform, suggesting a cellular selectivity based on the α-subunits. The effect on noninactivating currents may be responsible for the decrease of spontaneous action potential frequency. Long-term cellular incubation with testosterone did not modify noninactivating currents density in GH3 cells. It is remarkable that 5β-DHT, a reductase metabolite with weak androgenic activity, was the most efficient blocker.