Short-duration therapeutic hypothermia causesprompt connexin43 gap junction remodelingin isolated rabbit hearts

Abstract

Background: Whether connexin43 gap junctions (Cx43 GJs) and spatial heterogeneity of conduction velocity(CV) restitutions are altered in hearts during moderate (MH; 33°C) and severe (SH; 30°C) hypothermia remainsunclear.Methods and Results: Using an optical mapping system, ventricular CV was evaluated by S 1 pacing in 29Langendorff-perfused isolated rabbit hearts at baseline (37°C, n=9), 30-min MH (n=6), 30-min SH (n=9), andrewarming (R, 30-min SH followed by 30-min 37°C, n=5). After CV evaluation, myocardium was collected to measurethe level and distribution of non-phosphorylated (NP-Cx43) and total (T-Cx43) Cx43 by immunoblotting andimmunoconfocal microscopy. In 6 additional hearts, Cx43 GJ remodeling was evaluated at 30-min SH with (n=3)or without (n=3) pretreatment of a protein kinase C (PKC) inhibitor. CV slowing and spatial heterogeneities ofCV restitutions were enhanced in MH and SH hearts. NP-Cx43 was downregulated in MH (P=0.002) and SH(P<0.001) hearts. NP-Cx43 levels among 4 different ventricular sites became inhomogeneous in MH (P=0.017)and SH (P=0.046) hearts. However, T-Cx43 levels were unchanged. The percentages of lateralized NP- andT-Cx43 were increased in MH, SH, and R hearts. Pretreatment of PKC inhibitor attenuated SH-induced NP-Cx43lateralization (P=0.0495).Conclusions: Short-duration (30 min) therapeutic hypothermia causes prompt Cx43 GJs remodeling, in whichthe PKC pathway is involved. Rewarming abolished hypothermia-induced conduction disturbance, while Cx43GJs lateralization did not completely recover.