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 activati ng delayed rectifier channel and a HERG-like channel, a slowly activat ing potassium channel with biophysical properties identical to those o f 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 b ecome very slow when the depolarization starts from a very negative ho lding potential. In addition, extracellular Mg2+ and Ni2+ strongly slo w down activation. 4. Application of acetylcholine induces a fast bloc k of the current when recorded in the perforated patch mode. This bloc k is presumably mediated by Ca2+, as about 1 mu m intracellular Ca2+ c ompletely abolished h-eag outward current. 5. When cells were grown in the presence of 10 mu M retinoic acid in order to synchronize the cel l 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 channe l was expressed more abundantly. Downregulation of h-eag by long-term exposure to retinoic acid was paralleled by a right shift in the activ ation 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 cell s express in a cell cycle-dependent manner an [Mg2+](0)-dependent pota ssium channel (h-eag) which is blocked by submicromolar concentrations of intracellular Ca2+.