Fig. 4. Effect of Q/E mutations in SNAP-25 on the extent of exocytosis in adrenal chromaffin cells measured using amperometry. Adrenal chromaffin cells were transfected with a plasmid-encoding GFP-BoNT/E light chain along with the Em2 plasmid or Em2 containing the double Q/E mutations. After 3-5 days the cells were stimulated by local application of 20 µM digitonin and 10 µM Ca²⁺ and responses measured using carbon-fibre amperometry. Non-transfected cells were assayed as controls in the same dishes as GFP-expressing transfected cells and using the same carbon-fibres. (A) Mean numbers of amperometric spikes elicited in BoNT/E light-chain expressing cells (n=9 cells) compared to controls (n=10 cells) in the same dishes. (B) Mean numbers of spikes in control cells (n=39) or in cells co-transfected with Em2 (n=31 cells) or Em2 containing the double Q/E mutations (n=40 cells). Typical traces are shown from a non-transfected cell (C) or from cells co-transfected with GFP-BoNT/E light chain and Em2 (D) or the double Q/E mutant (E).