SUR1-TRPM4 channels, not KATP, mediate brain swelling following cerebral ischemia

Background: Preclinical and emerging clinical data show that glibenclamide reduces space occupying edema and brain swelling following cerebral ischemia. Glibenclamide is a potent inhibitor of numerous sulfonylurea receptor (SUR)-regulated channels, including K-ATP (SUR1-KIR6.2, SUR2A-KIR6.2, SUR2B-KIR6.2, SUR2B-KIR6.1) and SUR1-TRPM4. Here, we used molecularly specific oligodeoxynucleotides (ODNs) to investigate the role of various SUR-regulated ion channel subunits in post-ischemic brain swelling. Methods: Focal cerebral ischemia was induced in adult male rats by permanent middle cerebral artery occlusion (pMCAo). We used this model to study the effects of antisense-ODNs (AS-ODNs) directed against Abcc8/SUR1, Trpm4/TRPM4, Kcnj8/KIR6.1 and Kcnj11/KIR6.2 on hemispheric swelling, with sense or scrambled ODNs used as controls. We used antibody-based Forster resonance energy transfer (immuno-FRET) and co-immunoprecipitation to study the co-assembly of SUR1-TRPM4 heteromers. Results: In the combined control groups administered sense or scrambled ODNs, pMCAo resulted in uniformly large infarct volumes (mean +/- SD: 57.4 +/- 8.8 %; n = 34) at 24 h after onset of ischemia, with no effect of AS-ODNs on infarct size. In controls, hemispheric swelling was 23.9 +/- 4.1 % (n = 34), and swelling was linearly related to infarct volume (P < 0.02). In the groups administered anti-Abcc8/SUR1 or anti-Trpm4/TRPM4 AS-ODN, hemispheric swelling was significantly less, 11.6 +/- 3.9 % and 12.8 +/- 5.8 % respectively (P < 0.0001), and the relationship between infarct volume and swelling was reduced and not significant. AS-ODNs directed against Kcnj8/KIR6.1 and Kcnj11/KIR6.2 had no significant effect on hemispheric swelling (23.3 +/- 5.4 % and 22.9 +/- 5.8 % respectively). Post-ischemic tissues showed co-assembly of SUR1-TRPM4 heteromers. Conclusions: Post-ischemic hemispheric swelling can be decoupled from infarct volume. SUR1-TRPM4 channels, not K-ATP, mediate post-ischemic brain swelling.