Effects of diminished expression of connexin43 on gap junction number and size in ventricular myocardium

Abstract

Gap junction number and size vary widely in cardiac tissues with disparate conduction properties. Little is known about how tissue-specific patterns of intercellular junctions are established and regulated. To elucidate the relationship between gap junction channel protein expression and the structure of gap junctions, we analyzed Cx43 +/- mice, which have a genetic deficiency in expression of the major ventricular gap junction protein, connexin43 (Cx43). Quantitative confocal immunofluorescence microscopy revealed that diminished Cx43 signal in Cx43 +/- mice was due almost entirely to a reduction in the number of individual gap junctions (226 +/- 52 vs. 150 +/- 32 individual gap junctions/field in Cx43 +/+ and +/- ventricles, respectively; P < 0.05). The mean size of an individual gap junction was the same in both groups. Immunofluorescence results were confirmed with electron microscopic morphometry. Thus when connexin expression is diminished, ventricular myocytes become interconnected by a reduced number of large, normally sized gap junctions, rather than a normal number of smaller junctions. Maintenance of large gap junctions may be an adaptive response supporting safe ventricular conduction.

N-cadherin haploinsufficiency affects cardiac gap junctions and arrhythmic susceptibility

“…Hence, reduced levels of N-cadherin may alter the cytoskeleton leading to decreased stability of gap junctions at the cell surface. Another possibility is that N-cadherin-mediated cell-cell adhesion brings the plasma membranes in close apposition thus creating a localized region of low shear stress, which may be particularly important for assembly and maintenance of large Cx43 plaques (19). Although heart function and structure appear normal in the N-cadherin heterozygous mice, subtle changes in mechanical coupling due to reduce N-cadherin-mediated adhesion could affect localized regions of the sarcolemma creating a less favorable environment for large Cx43 plaques.…”

“…The double-stained sections were viewed and photographed with Zeiss LMS510 Meta confocal microscope. Immunofluorescent signal was analyzed by quantitative confocal microscopy using methods validated in previous studies (16,19,20). This method is specifically designed to measure the amount of signal at cell-cell junctions by quantifying the number of pixels concentrated in clusters showing high-intensity fluorescence.…”

Targeted Activation of c-Jun N-terminal Kinase in Vivo Induces Restrictive Cardiomyopathy and Conduction Defects

“…Immunohistochemistry-Immunostaining of Cx43 and cadherins was performed using paraffin embedded sections as previously described (23). Double labeling of Cx43 and ZO-1, as well as fibronectin immunostaining, was performed using frozen ventricular sections as described (24).…”

c-Jun N-Terminal Kinase Activation Mediates Downregulation of Connexin43 in Cardiomyocytes

“…34 Ultrathin (50-to 100-nm) sections were cut in a plane parallel to the long axis of the myocytes and analyzed according to methods used in previous studies. 34 Ten regions from control papillary muscle and epicardium were analyzed, and 20 regions from transgenic hearts were analyzed because of the marked reduction in gap junctions in transgenic hearts. The total number of gap junction profiles was counted in each region and expressed as a function of total tissue area.…”