Non-SG fusion is not blocked by antibodies against PI(3)P and PI(4)P. In whole-cell recording, antibodies (1:100 dilution) were added to the cytoplasmic (pipette) solution, which was dialyzed into cells for 5 min before Ca²⁺ was infused to trigger fusion. (A) A typical record from an RBL cell. The Ca²⁺-activated conductance rise was used to define the t₀ point. (B) The rise of capacitance was well described by the delayed monoexponential function given in the figure. The variable k₂ is the rate constant used for statistical analysis. The number of the data points was reduced to highlight the fitted curve. Antibodies against PI(3)P (C), PI(4)P (D), and both (E) fail to block non-SG fusion.