Endogenous PIP₂ dilates cerebral arteries via BK channels. Diameter traces from de-endothelized arteries after developing myogenic tone. (A) In the presence of 2 μM Ro 31-8220 and 0.2 μM thapsigargin, PLC inhibition (25 μM U73122) causes a robust dilation (+15.1%), which is further increased by 5 nM wortmannin. Maximal dilation is evoked by Ca²⁺-free solution. (B) BK channel block (0.3 μM paxilline) reduces diameter (−13%) and almost totally blunts U73122 and wortmannin actions. In A and B, a vertical line indicates the time at which Ro 31-8220 and thapsigargin were applied; horizontal lines help to visualize diameter changes. (C) Averaged diameters; **, P < 0.01; *, P < 0.05; n = 4.