Voltage-gated K+ channels in the mouse interleukin 3-dependent cell line, FDC-P2.

The electrical properties of a mouse interleukin (IL)-3-dependent cell line, FDC-P2, were examined using the tight-seal whole-cell clamp technique. Under current clamp conditions with 140 mM K+ in the pipette, the cells had a resting potential of approximately -30 mV. Under voltage-clamp conditions, a transient outward current was elicited upon depolarization from a holding potential of -80 mV. The current was activated at potentials more positive than -10 mV and had a delayed-rectifying property. It showed rapid activation and slow inactivation during command steps. The current was abolished by Cs+ in the pipette, indicating that K+ is the charge carrier. The K+ current was suppressed by tetraethylammonium with Ki of less than 0.1 mM and was not affected by scorpion toxin. Recovery from inactivation was steeply voltage dependent: As the holding potential was more hyperpolarized, the recovery became faster. Thus, with a holding potential of -80 mV, the current showed slight use-dependent inactivation, while the current decreased prominently by repetitive depolarization at a holding potential of -40 mV. These properties of the K+ current are similar to those of the l-type K+ channel current in mature T lymphocytes. The K+ current in FDC-P2 cells was dramatically reduced after culture in the IL-3-free medium for 1-2 days. When IL-3 was re-added to the medium, the current was re-expressed. These observations suggest that expression of the K+ current depends on extracellular IL-3, and that the current may play some roles in proliferation of these cells.