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Abstract
AbstractA
Gap junctions are clusters of double-membrane channels formed by two hemi-channel transmembrane protein structure termed connexons. Each connexon is made up of six transmembrane protein subunits named ”connexins” (Cx) (Di et al. 2005).
All connexins share a common structure and composition consisting of 4 transmembrane domains which separate 2 extracellular domains from 3 cytoplasmic portions. The latter cytoplasmic domains are specific to each Cx species and control the gating behavior of Cx channels. Four domains span across the cell membrane anchor the polypeptide, form the channel pore and determine the functional properties of Cx channels. The two extracellular domains are rigid and extend about 2 nm into the extracellular space to dock with those of a anther connxon from an opposing cell (Richard 2005).
Several physiological, pharmacological, and dietary factors alter the expression of connexins. For example, the expression of Cx32 and Cx26 in hepatocytes is increased by glucocorticoids (Kwiatkowski et al. 1994). Estrogen increases Cx43 transcription through estrogen-responsive elements (Yu et al. 1994). Cyclic adenosine monophosphate (cAMP) and glucagon increase Cx32 and Cx43 transcription (Saez et al. 1986).
Key words : connexin, keratinization, psoriasis, skin tumours, hearing loss, gap junction.