Regulation of neuronal connexin-36 channels by pH

Abstract

Neurotransmission through electrical synapses plays an important role in the spike synchrony among neurons and oscillation of neuronal networks. Indeed, electrical transmission has been implicated in the hypersynchronous electrical activity of epilepsy. We have investigated the influence of intracellular pH on the strength of electrical coupling mediated by connexin36 (Cx36), the principal gap junction protein in the electrical synapses of vertebrates. In striking contrast to other connexin isoforms, the activity of Cx36 channels decreases following alkalosis rather than acidosis when it is expressed in Xenopus oocytes and N2A cells. This uncoupling of Cx36 channels upon alkalinization occurred in the vertebrate orthologues analyzed (human, mouse, chicken, perch, and skate). While intracellular acidification caused a mild or moderate increase in the junctional conductance of virtually all these channels, the coupling of the skate Cx35 channel was partially blocked by acidosis. The mutational analysis suggests that the Cx36 channels may contain two gating mechanisms operating with opposing sensitivity to pH. One gate, the dominant mechanism, closes for alkalosis and it probably involves an interaction between the Cand N-terminal domains, while a secondary acid sensing gate only causes minor, albeit saturating, changes in coupling following acidosis and alkalosis. Thus, we conclude that neuronal Cx36 channels undergo unique regulation by pH i since their activity is inhibited by alkalosis rather than acidosis. These data provide a novel basis to define the relevance and consequences of the pH-dependent modulation of Cx36 synapses under physiological and pathological conditions. alkalosis ͉ electrical synapses ͉ intracellular pH ͉ pH gating ͉ gap junction

Dual Oxidase 2 (Duox2) Regulates Pannexin 1-mediated ATP Release in Primary Human Airway Epithelial Cells via Changes in Intracellular pH and Not H2O2 Production

“…In voltage clamp studies, it has been shown that Panx1 channels can be opened by positive transmembrane potentials (8,9,42) and that they are highly mechanosensitive, resulting in increased open probability by mechanical stress (8,43,44). Intracellular acidification correlates negatively with the open probability of many connexin channels (45,46) via identified intracellular regions shown to participate in pH gating as well as pH-induced changes in the conformation of Cx43 hemichannels by atomic force microscopy (47,48). Interestingly, CO 2 perfusion also abolished the conductance of Panx1 currents in oocytes (9), which is in accordance with our findings on hand showing that lowering of pH i leads to an inhibition of Panx1 currents (Fig.…”

Pannexins, distant relatives of the connexin family with specific cellular functions?

“…Intracellular acidification negatively influences the probability of many Cx channels (168,169) being open. In addition, for Panx1, induction of low intracellular pH by CO 2 perfusion abolishes the conductance.…”

Chemical synaptic and gap junctional interactions between principal neurons: Partners in epileptogenesis

“…Freeze-fracture replica immunogold labeling (FRIL) has conclusively shown a gap junction on a hippocampal mossy fiber axon (Hamzei-Sichani et al, 2007); this gap junction contained connexin36, the most abundant known gap junction protein in the brain (Condorelli et al, 2000). [It was, however, somewhat surprising that connexin36 was present: VFO is potentiated by alkaline conditions (Draguhn et al, 1998), whereas connexin36 channels close with alkaline conditions (González-Nieto et al, 2008); additionally, VFO persists in connexin36 knockout mice (Hormuzdi et al, 2001). One would therefore expect different connexins to be present in axons.]…”