Figure 2
BVT.12777 activates a tolbutamide-sensitive K+ current A, the upper trace shows a current clamp recording of a CRI-G1 cell following dialysis with a 5 mM ATP-containing solution. In this and subsequent current clamp figures the trace begins approximately 5 min after formation of the whole-cell configuration. Application of BVT.12777 (100 μM) for the time indicated hyperpolarized the cell from -50 mV to -76 mV, an action readily reversed by tolbutamide (100 μM), which returned membrane potential to -54 mV. Washout of all drugs from the bath resulted in a membrane potential of -70 mV, indicating the lack of reversibility of BVT.12777. The lower plot is the current-voltage relationship for the voltage clamped currents. Cells were voltage clamped at -50 mV and 10 mV steps of 100 ms duration were applied every 200 ms (range -120 to -30 mV). BVT.12777 increased the membrane conductance relative to control and tolbutamide reversed this BVT.12777-induced conductance increase with a reversal potential of -78 mV. B, cell-attached recording from a CRI-G1 cell, at 10 mV applied to the recording pipette. Single channel openings are shown as downward deflections. Addition of 100 μM BVT.12777 induced an increase in channel activity (Nf.Po) from 0.17 in control to 0.31, and 1.25 at 10 and 20 minutes respectively, after BVT addition. Application of 100 μM tolbutamide induced a substantial inhibition of activity (to 0.02), which was reversed on washout of all drugs, with activity increasing to 0.74. The symbol C refers to the closed state of the channel in this and subsequent figures. C, diary plot of Nf.Po against time from cell-attached experiments in the presence and absence of BVT.12777, where channel activity was calculated every 2 minutes. Each point is the mean of 4–7 separate determinations.