Disease relevance of Gja5

• Sepsis up-regulates the expression of connexin 40 in rat aortic endothelium [1].
• To begin to analyze Cx40 expression, we isolated a 3.3-kb rat Cx40 cDNA by hybridization screening of a bacteriophage library prepared from BWEM cells and isolated corresponding mouse genomic clones from a bacterial artificial chromosome library [2].
• Under hypertensive conditions (ie, in spontaneous hypertensive rats and in transgenic rats that exhibit hypertension due to expression of an exogenous renin gene), we found a 3.1-fold increase in Cx40 expression, compared with normal myocardium [3].
• Luciferase assays of the natural rCx40 proximal promoter or mutated derivatives in Cx40-expressing (NCM, primary rat neonatal cardiomyocytes and A7r5, rat smooth muscle embryonic thoracic aorta cells) and -nonexpressing cells (N2A, mouse neuroblastoma cells) revealed that all sites are contributing to basal promoter activity [4].

High impact information on Gja5

• Similarly, antibody against Cx40 coimmunoprecipitated Cx43 from the same connexon fraction but only Cx40 from Cx (monomer) fractions [5].
• Connexin (Cx) 43 and Cx40 are coexpressed in several tissues, including cardiac atrial and ventricular myocytes and vascular smooth muscle [5].
• Three connexins, Cx43, Cx40, and Cx37, have been found by protein or mRNA analysis to be prominent in mammalian blood vessels, but electrophysiological characterization of gap junction channels in freshly isolated vascular smooth muscle cells (SMCs) has not previously been reported [6].
• Our data indicate that basilar artery SMCs are coupled in vivo in a richly complex manner, involving Cx43, Cx40, and other large-conductance channels, and that a significant number of couplings involve putative nonhomotypic channels [6].
• Up to 3 connexin types, connexin40 (Cx40), Cx37, and Cx43 may be expressed in vascular endothelium according to vascular site, species, and physiological conditions [7].

Biological context of Gja5

• Treatment with candesartan, but not the combination of hydralazine and hydrochlorothiazide, significantly increased the expression of Cx37 and Cx40, although blood pressure decreased similarly [8].
• The principal gap junction protein of intercellular communication, connexin, was investigated to determine the effects of high glucose concentrations on the expression of endothelial-specific connexins (Cx37, Cx40, and Cx43), connexin phosphorylation pattern, and GJIC activity [9].
• The resulting luciferase activity determinations suggested that an area of 300 bp 5' of the transcription start site acted as a basal promoter for Cx40 and that there was a strong negative regulatory element in the region from +100 to +297 [2].
• Kinetics of Cx40 voltage gating were examined at peak voltages > or =100 mV, and decay time constants changed e-fold per 17.6 mV for Vj > +/-40 mV [10].
• To identify transcriptional regulatory elements in the Cx40 promoter region, a series of DNA deletion fragments flanking exon I was prepared, subcloned adjacent to a luciferase reporter gene, and used for transient transfections of BWEM, SHM, and N2A cells [2].

Anatomical context of Gja5

• In the present study, we tested whether the polymicrobial sepsis induced by cecal ligation and perforation in the rat alters the expression of the connexins present in the vascular endothelium (i.e., Cx37, Cx40, and Cx43) [1].
• Immunoelectron microscopic visualization of the gap junction protein connexin 40 in the mammalian heart [11].
• High-resolution immunohistochemistry localized Cx40 to the end of endothelial cell projections at myoendothelial gap junctions [12].
• In rabbit, cx40 was found in gap junctions between myocytes of the right atrium as well as in the false tendons of the left ventricle [11].
• Cx43 and Cx40 plaque diameters were 0.9 +/- 0.1 and 0.8 +/- 0.1 (SE) microns, respectively, in the endothelial layer and 0.5 +/- 0.1 and 0.5 +/- 0.1 microns, respectively, in the smooth muscle [13].

Associations of Gja5 with chemical compounds

• These data suggest that the HKH motif at positions 15-17 is important to the conformational structure of the putative voltage sensor and spermine receptor of Cx40, without causing significant alteration of the electrostatic surface charge potentials that contribute to the ion selectivity of this gap junction channel [14].
• Spermine blocks connexin40 (Cx40) gap junctions, and two cytoplasmic amino-terminal domain glutamate residues are essential for this inhibitory activity [14].
• Cultured neonatal rat cardiomyocytes were exposed for 24 h to increasing concentrations of noradrenaline (1-10000 nM) (physiological agonist at alpha and beta-adrenoceptors), resulting in significantly increased Cx43-expression, while Cx40 was unaffected [15].
• In additional in vivo experiments, adult rats were subjected to 24-h infusion of isoproterenol or phenylephrine showing again significant increase in Cx43 but not Cx40 [15].
• RESULTS: 43Gap 27, a peptide homologous to the second extracellular loop of connexin 43, partially inhibited the L-NAME- and indomethacin-resistant RBF response to acetylcholine, whereas 40Gap 27, homologous to the second extracellular loop of connexin 40, abolished the response [16].

Regulatory relationships of Gja5

• In the present study, we demonstrate, using dual whole-cell voltage-clamp techniques, that coexpression of connexin (Cx) 40 and Cx43 rendered cells more sensitive to uncoupling by halothane than cells that express only Cx40 or only Cx43 [17].

Other interactions of Gja5

• It remains to be clarified whether these changes in Cx37 and Cx40 are related to endothelial function, particularly that attributable to EDHF [8].
• Twenty percent stretch of cultured rat cardiomyocytes caused a 3-fold increase in Cx43 mRNA levels by 2 h. c-fos mRNA levels increased after 30 min of stretch, whereas Cx40, Cx37, and GADPH mRNA did not change [18].
• In addition, we report the expression of Cx30, Cx30.3, Cx40, and Cx45 in rat keratinocytes, highlighting the complexity of the connexin complement in rat epidermis [19].

Analytical, diagnostic and therapeutic context of Gja5

• Restriction mapping, sequencing, and comparison to the rat cDNA showed that the mouse Cx40 gene contained a short first exon, an 11.4-kb intron, and a second exon containing the complete coding region and 3'-UTR [2].
• We used polymerase chain reaction (PCR) amplification and cDNA library screening to clone DNA encoding a novel member of this gene family, rat connexin40 (Cx40) [20].
• Northern blots demonstrate that Cx40 is expressed in multiple tissues (including lung, heart, uterus, ovary, and blood vessels) and in primary cultures and established lines of vascular smooth muscle cells [20].
• Connexons (hemichannels), which were isolated from these cells by density centrifugation and immunoprecipitated with antibody against Cx43, contained Cx40 [5].
• Two of these conductances, 80 to 120 pS and 150 to 200 pS, corresponded to the major conductance states for homotypic channels formed from Cx43 or Cx40, which we confirmed were present in smooth muscle by immunofluorescence analysis [6].

References