Negative charge and inositol moiety both contribute to phosphoinositide activation of myocyte BK channels. (A) Unitary currents from I/O patches exposed to control or phospholipids that differ in headgroup structure. Arrowheads, baseline; upward deflections, channel openings. (B) BK channel potentiation is a direct function (r = 0.99) of negative charge in the phospholipid headgroup. (a) PI vs. PI5P: P < 0.001; (b) PI vs. PIP₂: P < 0.001; (c) PI5P vs. PIP₂: P < 0.001; (d) PI vs. PIP₃: P < 0.001; (e) PI5P vs. PIP₃: P < 0.001; (f) PIP₂ vs. PIP₃: P < 0.05; n = 3–12. (C) I/O recordings and (D) averaged data show that coapplication of 0.1 mg/ml poly-l-lysine reduces PIP₂ activation of BK channels; n = 3. (E) PS and PI (net charge ≈ −1) cause more robust activation than that evoked by the neutral PC. However, PI is more effective than PS. (a) PC vs. PS: P < 0.05; (b) PC vs. PI: P < 0.001; (c) PS vs. PI: P < 0.001; n = 3–6. All phospholipid species had dipalmitoyl chains. V = 40 mV; Ca²⁺_i = 0.3 μM.