OPENING OF LARGE-CONDUCTANCE CALCIUM-ACTIVATED POTASSIUM CHANNELS BY THE SUBSTITUTED BENZIMIDAZOLONE NS004

1. We used electrophysiological techniques to examine the effects of - hydroxyphenyl)-1,3-dihydro-2H-benzimidazole-2-one (NS004) on large-con ductance calcium-activated potassium (BK) channels. 2. We used recordi ngs from excised membrane patches (cell-attached and inside-out single -channel configurations) and whole-cell patch-clamp recordings to exam ine the effects of NS004 on single BK channels and whole-cell outward currents, respectively, in rat GH3 clonal pituitary tumor cells. We al so tested NS004 on voltage-clamped BK channels isolated from rat brain plasma membrane preparations and reconstituted into planar lipid bila yers. Finally, we used two-electrode voltage-clamp techniques to study the effects of NS004 on currents expressed in Xenopus laevis oocytes by the recently described Sla BK clone from Drosophila. 3. In GH3 cell s and in Xenopus oocytes expressing the Slo gene product NS004 produce d an increase in an iberiotoxin- or tetraethylammonium-sensitive whole -cell outward current, respectively. NS004 produced a significant incr ease in the activity of single GH3 cell BK channels and rat brain BK c hannels reconstituted into planar lipid bilayers. In both systems this was characterized by an increase in channel mean open time, a decreas e in interburst interval, and an apparent increase in channel voltage/ calcium sensitivity. 4. These data indicate that NS004 could be usefu l for investigating the biophysical and molecular properties of BK cha nnels and for determining the functional consequences of the opening o f BK channels.