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

Roman Meyer and Stefan H. Heinemann

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 µM intracellular Ca²⁺ completely abolished h-eag outward current.

5. When cells were grown in the presence of 10 µM 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. Down-regulation 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 µM 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⁺]_o-dependent potassium channel (h-eag) which is blocked by submicromolar concentrations of intracellular Ca²⁺.

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