Characterization of an eag-like potassium channel in human neuroblastoma cells

1. SH-SY5Y human neuroblastoma cells were investigated with whole-cell and perforated patch recording methods. 2. Besides a quickly activating delayed rectifier channel and a HERG-like channel, a slowly activating potassium channel with biophysical properties identical to those of rat eag (r-eag) channels was detected, here referred to as h-eag. 3. h-eag shows a marked Cole-Moore shift, i.e. the activation kinetics become very slow when the depolarization starts from a very negative holding potential. In addition, extracellular Mg2+ and Ni2+ strongly slow down activation. 4. Application of acetylcholine induces a fast block of the current when recorded in the perforated patch mode. This block is presumably mediated by Ca2+, as about 1 mu m intracellular Ca2+ completely abolished h-eag outward current. 5. When cells were grown in the presence of 10 mu M retinoic acid in order to synchronize the cell line in the G1 phase of the cell cycle, h-eag current was reduced to less than 5% of the control value, while the delayed rectifier channel was expressed more abundantly. Downregulation of h-eag by long-term exposure to retinoic acid was paralleled by a right shift in the activation potential of HERG-like channels. 6. Acute application of 10 mu M retinoic acid blocked the delayed rectifier channel but enhanced the h-eag current. 7. Thus, our results show that human neuroblastoma cells express in a cell cycle-dependent manner an [Mg2+](0)-dependent potassium channel (h-eag) which is blocked by submicromolar concentrations of intracellular Ca2+.