Figure 4.

The effect of exogenous PIP₂ on the ATP sensitivity. (A) The time course of PIP₂ activation in an inside-out patch experiment. The patch was excised at the time indicated by the arrow. PIP₂ application is indicated by the hatched bar. (B) The inhibitory effect of ATP on K_ATP channels activated by PIP₂. PIP₂ (10 μM) was applied for 3 min before examining ATP sensitivity. The current traces in A and B were recorded in different patches. (C) The whole-cell K_ATP current activated by the pipette solution containing 100 μM PIP₂. After the application of positive pressure [≈10 cmH₂O (1 cm H₂O = 88 Pa)], the K_ATP current started to occur. The holding potential was −20 mV. The ramp pulse was applied from −140 mV to 0 mV. BaCl₂ (5 mM) was applied to examine the reversal potential (≈−85 mV). (D) Dose-inhibition curves for ATP. ○, Control; □, 40 s after the application of 10 μM PIP₂. ▵, 3 min after 10 μM PIP₂ application. The Hill equation fitted to data points is indicated in the legend of Fig. 5. IC₅₀ values are indicated in the text.