Hypoxia causes connexin 43 internalization in neonatal rat ventricular myocytes

Abstract

Gap junctions produce low resistance pathways between cardiomyocytes and are major determinants of electrical conduction in the heart. Altered distribution and function of connexin 43 (Cx43), the major gap junctional protein in the ventricles, can slow conduction, and thus contribute to arrhythmogenesis in experimental models such as ischemic rat heart and pacing-induced atrial fibrillation. The mechanisms underlying reduced gap junctional density and conductance during ischemia may involve decreased Cx43 synthesis, increased degradation and/or Cx43 migration into areas which do not contribute to intercellular communication. To test more rigorously the hypothesis that hypoxia resulting from ischemia causes Cx43 internalization, we infected neonatal rat ventricular myocytes (NRVM) with a Cx43-GFP chimera, which enabled us to investigate by means of confocal microscopy the effect of hypoxia (1% O 2 for 5 h) on Cx43 distribution in live cardiomyocytes. Importantly, this protocol permitted each culture to serve as its own control. To this end we used life confocal microscopy analysis to determine in the same pair of myocytes the effects of hypoxia on Cx43-GFP distribution at the gap junctional (GJ) and non-GJ areas. In support of this hypothesis, we found that compared to normoxia, 5 h of hypoxia reduced the Cx43-GFP signal at the GJ areas (defined as the border area) and caused a corresponding increase in the Cx43-GFP signal at the non-border areas, thus providing an additional explanation for the intercellular uncoupling during ischemic conditions.

Connexin 43 stabilizes astrocytes in a stroke-like milieu to facilitate neuronal recovery

“…Cx43 shows a strong ability to maintain the normal shape and function of astrocytes. The dynamic distribution of Cx43, consisting of the transport of Cx43 into the cytoplasmic membrane and internalization of Cx43, takes place by regular turnover [29] and in abnormal states of the cells [30][31][32] . The alterations in the dynamic distribution of Cx43 in cells undergoing morbidity could be normal in certain roles.…”

Connexin 43 is an emerging therapeutic target in ischemia/reperfusion injury, cardioprotection and neuroprotection

“…During short periods of hypoxia (up to 15 minutes) Cx43 content remains unchanged (Matsumura et al, 2006;Zeevi-Levin et al, 2005). With prolonged hypoxia (several hours), downregulation of Cx43 at gap junctions occurs (Danon et al, 2010), Cx43 is internalized (Sato et al, 2009) and subsequently the total cellular Cx43 content decreases (Zeevi-Levin et al, 2005). …”

Increase of PPARδ by dopamine mediated via DA-1 receptor-linked phospholipase C pathway in neonatal rat cardiomyocytes

“…Primary cultures of neonatal rat cardiomyocytes were prepared by the modification of a previously described method (Danon et al, 2010). Briefly, under anesthesia with 5% isoflurane, hearts of 1-to 2-day-old Wistar rats were excised, cut into 1-2 mm pieces and predigested with trypsin to remove red blood cells.…”