Connexins are the proteins responsible of forming gap junctions. Six subunits are necessary to form a hemichannel or connexon anchored in the plasma membrane. Two hemichannels of adjacent cells form a gap junction. At present, there are, at least, 20 isoforms of connexins described. Particularly, mutations in Connexin 32 (Cx32) have been associated with the X-linked form of Charcot-Marie-Tooth disease (CMTX), a neurodegenerative illness affecting the peripheral nervous system. There is growing evidence that ATP is being released, under some stimulus, through hemichannels constituted either by connexins or pannexins. Using immunofluorescent methodology we have localized Connexin 32 (Cx32) in Schwann cells (SCs) of teased nerve fibers from mice sciatic nerve, concretely in the paranodal zones of nodes of Ranvier and in the Schmidt-Lantermann incisures. We have assayed to detect the release of ATP from mechanical and electrical stimulated nerve fibers through the Luciferin-Luciferase bioluminescent reaction using the Orca II and the ImagEM digital cameras (Hamamatsu). Under these conditions we found the maximal release of ATP in the paranodal zones of Schwann cells. Because Schwann cells express some forms of P2X and P2Y receptors, we hypothesize that, in physiological conditions, Schwann cells release ATP which would act as an autocrine signal.

We have expressed the human Cx32 (hCx32) in Xenopus laevis oocytes and we have measured simultaneously the electric currents supported by Cx32 and the release of ATP. We have recorded that hCx32 is permeable to ATP when is forming hemichannels. Five mutations of Cx32 have been tested for ATP release and in all mutations tested (hCx32S26L;hCx32 P87A; hCx32Del111-116;hCx32D178Y and hCx32 R220X) the ATP release was inhibited or completely abolished

In view of our results, we suggest that mutations of Cx32 described in CMTX disease may be due to an impairment of autocrine purinergic signalling, which should be a key process to maintain SCs in healthy conditions.