OLIGODENDROCYTES EXPRESS GAP JUNCTION PROTEINS CONNEXIN32 AND CONNEXIN45

Oligodendrocytes, the myelin-forming glia of brain, are connected by g ap junctions in situ and in culture. Cultured oligodendrocytes from ad ult bovine and porcine brains were studied using immunocytochemical, m olecular, and electrophysiological techniques in order to characterize the gap junction types. The expression of connexin32 was substantiate d by the detection of low, but significant, signals using connexin-spe cific probes in Northern and Western blot analyses. Connexin43, which comprises gap junctions in astrocytes, was not detectable in pure olig odendrocytic cultures; mRNAs of connexin40 and connexin37 and connexin 26 were also not detected. By means of two specific antibodies directe d to the recently cloned connexin45 and by RT-PCR we were able to iden tify this connexin as a second oligodendrocytic gap junction protein. Whole cell voltage clamp recording provided evidence for electrical co upling between pairs of cultured oligodendrocytes (mean junctional con ductance 3.9 nS, n = 38 pairs) and intracellular Lucifer Yellow inject ion indicated that oligodendrocytes were usually only weakly dye coupl ed, with spread generally being restricted to nearest neighbors. Unita ry conductances ranged from >20 to <150 pS with modes of distribution at about 100 to 120pS and 40 to 20 pS, respectively. These unitary con ductances are consistent with the channel events expected for connexin 32 and connexin45. The low degree of functional coupling between oligo dendrocytes in vitro corresponds with the low levels of connexin32 and connexin45 messenger RNAs and protein expression. (C) 1997 Wiley-Liss , Inc.