Abstract
It is becoming clear that in addition to gap junctions playing a role in cell–cell communication, gap junction proteins (connexins) located in cytoplasmic compartments may have other important functions. Mitochondrial connexin 43 (Cx43) is increased after ischemic preconditioning and has been suggested to play a protective role in the heart. How Cx43 traffics to the mitochondria and the interactions of mitochondria with other Cx43-containing structures are unclear. In this study, immunocytochemical, super-resolution, and transmission electron microscopy were used to detect cytoplasmic Cx43-containing structures and to demonstrate their interactions with other cytoplasmic organelles. The most prominent cytoplasmic Cx43-containing structures—annular gap junctions—were demonstrated to form intimate associations with lysosomes as well as with mitochondria. Surprisingly, the frequency of associations between mitochondria and annular gap junctions was greater than that between lysosomes and annular gap junctions. The benefits of annular gap junction/mitochondrial associations are not known. However, it is tempting to suggest, among other possibilities, that the contact between annular gap junction vesicles and mitochondria facilitates Cx43 delivery to the mitochondria. Furthermore, it points to the need for investigating annular gap junctions as more than only vesicles destined for degradation.
Highlights
Gap junction channels play a pivotal role in a vast number of physiological events by providing channels for the intercellular communication of regulatory molecules between cells [1]
We documented the presence of cytoplasmic connexin 43 (Cx43)-containing structures and we analyzed the details and frequency of interactions of mitochondria and lysosomes with annular gap junction vesicles
We found that the interactions between annular gap junctions and mitochondria were seen more frequently than between annular gap junctions and lysosomes
Summary
Gap junction channels play a pivotal role in a vast number of physiological events by providing channels for the intercellular communication of regulatory molecules between cells [1]. Gap junction channels are composed of gap junction proteins, termed connexins [2]. Connexin 43 (Cx43) gap junction protein, the most ubiquitously expressed connexin, is thought to be synthesized in the endoplasmic reticulum, oligomerized into a hemichannel in the Golgi [6] and transported to the cell surface in secretory vesicles. Gap junction channels aggregate to form gap junction plaques [1]. These gap junction plaques are composed of thousands of channels [6] and plaque size is determined by the number of hemichannels that are delivered to the membrane in secretory vesicles and aggregated on the surface to form these plaques [7]
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