Role of connexin 32 hemichannels in the release of ATP from peripheral nerves

Abstract

Extracellular purines elicit strong signals in the nervous system. Adenosine-5'-triphosphate (ATP) does not spontaneously cross the plasma membrane, and nervous cells secrete ATP by exocytosis or through plasma membrane proteins such as connexin hemichannels. Using a combination of imaging, luminescence and electrophysiological techniques, we explored the possibility that Connexin 32 (Cx32), expressed in Schwann cells (SCs) myelinating the peripheral nervous system could be an important source of ATP in peripheral nerves. We triggered the release of ATP in vivo from mice sciatic nerves by electrical stimulation and from cultured SCs by high extracellular potassium concentration-evoked depolarization. No ATP was detected in the extracellular media after treatment of the sciatic nerve with Octanol or Carbenoxolone, and ATP release was significantly inhibited after silencing Cx32 from SCs cultures. We investigated the permeability of Cx32 to ATP by expressing Cx32 hemichannels in Xenopus laevis oocytes. We found that ATP release is coupled to the inward tail current generated after the activation of Cx32 hemichannels by depolarization pulses, and it is sensitive to low extracellular calcium concentrations. Moreover, we found altered ATP release in mutated Cx32 hemichannels related to the X-linked form of Charcot-Marie-Tooth disease, suggesting that purinergic-mediated signaling in peripheral nerves could underlie the physiopathology of this neuropathy.

The membrane protein Pannexin1 forms two open-channel conformations depending on the mode of activation

“…The positive potentials required for Panx1 channel activation approximate the reversal potential for MgATP 2− and ATP 4− . Indeed, as indicated in a recent study of connexin hemichannels (38), a membrane potential of +80 mV is close to or even beyond the reversal potential for ATP. ATP flux through connexin hemichannels, which only open at extreme positive potentials, did not occur while the membrane potential was stepped to +80 mV.…”

Loss of Coupling Distinguishes GJB1 Mutations Associated with CNS Manifestations of CMT1X from Those Without CNS Manifestations

“…Such a critical molecule, if one exists, remains to be identified. However, one candidate is ATP, the release of which appears to be dependent on Cx32 hemichannels and is likely affected by mutations in GJB156. In this regard, this study has shown that the four PNS-only mutations, if they indeed obstruct the flux of larger molecules, could be useful in future studies aimed at determining which small molecules could be relevant to CMT1X pathology in peripheral nerve.…”

Enteric glial activity regulates secretomotor function in the mouse colon but does not acutely affect gut permeability

“…Very little is known about how Schwann cells influence the activity of sympathetic axons in the periphery. What is known suggests that myelinating Schwann cells do share some common features with enteric glia such as the expression of Sox10 and the ability to release neuroactive substances like ATP through hemichannels (Nualart-Marti et al 2013). However, there are also important differences between the specific mechanisms used by the two cell types.…”