CONNEXIN43 IS ANOTHER GAP JUNCTION PROTEIN IN THE PERIPHERAL NERVOUS-SYSTEM

That many cells express more than one connexin (Cx) led us to examine whether Cxs other than Cx32 are expressed in the PNS, In addition to C x32 mRNA, Cx43 and Cx26 mRNAs were detected in rat sciatic nerve by no rthern blot analysis. Cx43 mRNA, but not Cx26 mRNA, was expressed in b oth the primary Schwann cell culture and immortalized Schwann cell lin e (T93). The steady-state levels of the Cx43 mRNA in the primary Schwa nn cell culture increased 2.0-fold with 100 mu M forskolin, whereas th at of P-0 increased 7.0-fold. Immunoreactivity to Cx43 was detected on western blots of cultured Schwann cells, T93 cells, and sciatic nerve s but not on blots of PNS myelin. Immunohistochemical study using huma n peripheral nerves revealed that anti-Cx43 antibody stained cytoplasm around nucleus of Schwann cells but not myelin, confirming western bl ot results. Although P-0 expression was markedly decreased by crush in jury of the sciatic nerves, Cx43 expression showed no apparent change. Developmental profiles showed that Cx43 expression in the sciatic ner ve increased rapidly after birth, peaked at about postnatal day 6, and then decreased gradually to a low level. In adult rats, the Cx43 mRNA value was much lower than that of Cx32. These findings suggest that C x43 is localized in Schwann cell bodies and that, compared with P-0, i ts expression is less influenced by axonal contact and cyclic AMP leve ls. The high expression on postnatal day 6 indicates that Cx43 may be related to PNS myelination. Cx43 is another gap junction, but its func tion appears to differ from that of Cx32, as judged by the differences in their localization and developmental profiles.