Gap Junction Expression in Myelinating Cells
Gap junctions comprise intercellular channels which allow the direct exchange of small metabolites (glucose, nucleotides, amino acids, etc) as well as the transmission of ions for propagating electrical currents [for reviews see 1, 2]. Accumulating evidence indicates that the biophysical properties of the gap junction channels are variable according to the specific protein complement that forms the channel . The gap junction proteins, collectively called connexins, are oligomerized in hexamers (connexons) which form hemichannels in plasma membranes. When docked to a partner connexon a competent gap junction channel is formed which spans the two adjoining plasma membranes. At present thirteen members of the connexin family have been cloned and their tissue specific expression has been determined [for review see 1]. In the central and peripheral nervous system connexins are differentially expressed with respect to cell specificity and developmental stage . Oligodendrocytes and Schwann cells, the myelin forming cells in the peripheral and central nervous system, have been described to express connexin32 [4, 5], which was first identified and cloned form rodent and human liver cDNAs [ 6, 7]. The biophysical properties of the gap junction channel formed by connexin32 have been extensively studied. Cell lines, stabely transfected with the connexin32 gene revealed a unitary conductance of the connexin32 channel in the range of 120 pS, showed voltage dependence, and pH sensitivity [8, 9]. From a functional point of view it is of considerable interest that the connexin32 channel is permeable to second messenger including calcium and IP3, and that the strength of coupling is modulated by a PKA dependent phosphorylation .
KeywordsSchwann Cell Myelin Sheath Myelinating Cell Connexin32 Expression Connexin32 Gene
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