Objectives : Altered gap junctional coupling of ventricular myocytes plays an important role in arrhythmogenesis in ischemic heart disease. Since hypoxia is a major component of ischemia, we tested the hypothesis that hypoxia causes gap junctional remodeling accompanied by conduction disturbances. Methods : Cultured neonatal rat ventricular myocytes were exposed to hypoxia (1% O2) for 15 min to 5 h, connexin43 (Cx43) expression was analyzed, and conduction velocity was measured using the Micro-Electrode Array data acquisition system. Results : After 15 min of hypoxia, conduction velocity was unaffected, while total Cx43, including the phosphorylated and nonphosphorylated isoforms, was increased. After 5 h of hypoxia, total Cx43 protein was decreased by 50%, while the nonphosphorylated Cx43 isoform was unchanged. Confocal analyses yielded a 55% decrease in the gap junctional Cx43 fluorescence signal, a 55% decrease in gap junction number, and a 26% decrease in size. The changes in Cx43 were not accompanied by changes in mRNA levels. The reduction in Cx43 protein levels was associated with a ∼20% decrease in conduction velocity compared to normoxic cultures. Conclusions : Short-term hypoxia (5 h) decreases Cx43 protein and conduction velocity, thereby contributing to the generation of an arrhythmogenic substrate.
