Semi-quantitative comparison of SNAP25 isoform expression levels in human brain. A) Lysates prepared from post-mortem brain samples (pooled from 6 individual patients) were resolved by SDS-PAGE alongside various dilutions of HEK293T lysates from cells transfected with EGFP-SNAP25a, EGFP-SNAP25b or EGFP-SNAP23. Gels were transferred to nitrocellulose and immunoblotted using antibodies against SNAP25a (3067), SNAP25b (3068) or SNAP23. The position of EGFP-tagged and endogenous proteins are highlighted, and molecular weight markers are shown on the left side of all blots. B) The relative levels of SNAP25a, SNAP25b and SNAP23 in brain were calculated by comparison of band intensities to those of the respective EGFP-tagged proteins. Highest expression levels were for SNAP25b in cortex and this was given an arbitrary value of 1, with all other values expressed as a fraction of this.