Connexin Hemichannels

Synonyms

Gap junction hemichannels

Definition

Homeostasis is controlled by a myriad of extracellular, intracellular, and intercellular communication mechanisms. Typically, extracellular signals trigger intracellular signal transduction cascades. Several of these intracellular signals are subsequently propagated to adjacent cells. Such intercellular connections are formed by arrays of gap junctions. They are composed of two hemichannels of neighboring cells, which in turn are built up by six connexin (Cx) proteins (Fig. 1). More than 20 different connexin species have been identified. They are all designated based upon their molecular weight as predicted by cDNA sequencing and are expressed in a cell-type-specific way (Table 1). Among those, Cx43, with a molecular weight of 43 kDa, is the most widespread connexin species in vertebrate cells. Connexins share a similar structure consisting of four transmembrane domains, two extracellular loops, one cytosolic loop, one cytosolic...