Myocardial connexin-43 is upregulated in response to acute cardiac injury in rats

We aimed to explore whether myocardial intercellular channel protein connexin-43 (Cx43) along with PKCε and MMP-2 might be implicated in responses to acute cardiac injury induced by 2 distinct sublethal interventions in Wistar rats. Animals underwent either single chest irradiation at dose of 25 Gy or subcutaneous injection of isoproterenol (ISO, 120 mg/kg) and were compared with untreated controls. Forty-two days post-interventions, the hearts were excised and left ventricles were used for analysis. The findings showed an increase of total as well as phosphorylated forms of myocardial Cx43 regardless of the type of interventions. Enhanced phosphorylation of Cx43 coincided with increased PKCε expression in both models. Elevation of Cx43 was associated with its enhanced distribution on lateral surfaces of the cardiomyocytes in response to both interventions, while focal areas of fibrosis without Cx43 were found in post-ISO but not post-irradiated rat hearts. In parallel, MMP-2 activity was decreased in the former while increased in the latter. Cardiac function was maintained and the susceptibility of the hearts to ischemia or malignant arrhythmias was not deteriorated 42 days after interventions when compared with controls. Altogether, the findings indicate that myocardial Cx43 is most likely implicated in potentially salutary responses to acute heart injury.

Nonredundant Gap Junction Functions

The need for molecular heterogeneity of gap junction channel proteins in vivo has been enigmatic. Recently, functional replacement of one channel gene with another in mice and flies has revealed that cellular health depends not simply on gap junction communication but also requires the correct type of intercellular channel subunit.

Targeted Ablation of Connexin50 in Mice Results in Microphthalmia and Zonular Pulverulent Cataracts

In the ocular lens, gap junctional communication is a key component of homeostatic mechanisms preventing cataract formation. Gap junctions in rodent lens fibers contain two known intercellular channel-forming proteins, connexin50 (Cx50) and Cx46. Since targeted ablation of Cx46 has been shown to cause senile-type nuclear opacities, it appears that Cx50 alone cannot meet homeostatic requirements. To determine if lens pathology arises from a reduction in levels of communication or the loss of a connexin-specific function, we have generated mice with a targeted deletion of the Cx50 gene. Cx50-null mice exhibited microphthalmia and nuclear cataracts. At postnatal day 14 (P14), Cx50-knockout eyes weighed 32% less than controls, whereas lens mass was reduced by 46%. Cx50-knockout lenses also developed zonular pulverulent cataracts, and lens abnormalities were detected by P7. Deletion of Cx50 did not alter the amounts or distributions of Cx46 or Cx43, a component of lens epithelial junctions. In addition, intercellular passage of tracers revealed the persistence of communication between all cell types in the Cx50-knockout lens. These results demonstrate that Cx50 is required not only for maintenance of lens transparency but also for normal eye growth. Furthermore, these data indicate that unique functional properties of both Cx46 and Cx50 are required for proper lens development.

Three-Dimensional Structure of the Gap Junction Connexon and Intercellular Channel

Gap junctions are specialized cell-cell contact areas by which cells communication with each other. Within these contact areas are tens to thousands of membrane channels. A gap junction membrane channel (also referred to as an intercellular channel) is unique among membrane channels in that it is composed of two oligomers with each of two adjacent tissue cells contributing one oligomer (called a connexon or hemichannel). The pore of the intercellular channel controls the passage of small molecules and ions from one cell to another.We are interested in how the structure and surface topology of the gap junction connexon at its extracellular surface influences the docking and formation of an intercellular communicating channel. It has been demonstrated that connexons made from some connexins will dock and form functional channels with some but not all connexons made from other isoforms. This selectivity is surprising considering that the primary sequences of the docking domains are highly conserved.