Nitric oxide regulation of colonic epithelial ion transport: a novel role for enteric glia in the myenteric plexus

Abstract

Non-technical summary The enteric nervous system of the gastrointestinal tract regulates all the functions of the gut. Enteric neurons are surrounded and outnumbered by enteric glial cells, whose functions are not well understood. Digestive and defensive functions of the gut require the secretion of fluid into the lumen in a regulated manner. Fluid is controlled by the secretion or absorption of ions across the epithelium. Here we have identified a physiological role for enteric glia of the colon in the regulation of fluid balance, through the production of the gaseous mediator nitric oxide. Enteric glia work in concert with enteric nerves by using nitric oxide to regulate the movement of ions across the wall of the colon, thereby affecting water movement and hence digestion and host defence.Abstract Enteric glia are increasingly recognized as important in the regulation of a variety of gastrointestinal functions. Here we tested the hypothesis that nicotinic signalling in the myenteric plexus results in the release of nitric oxide (NO) from neurons and enteric glia to modulate epithelial ion transport. Ion transport was assessed using full-thickness or muscle-stripped segments of mouse colon mounted in Ussing chambers. The cell-permeant NO-sensitive dye DAR-4M AM and amperometry were utilized to identify the cellular sites of NO production within the myenteric plexus and the contributions from specific NOS isoforms. Nicotinic receptors were localized using immunohistochemistry. Nicotinic cholinergic stimulation of colonic segments resulted in NO-dependent changes in epithelial active electrogenic ion transport that were TTX sensitive and significantly altered in the absence of the myenteric plexus. Nicotinic stimulation of the myenteric plexus resulted in NO production and release from neurons and enteric glia, which was completely blocked in the presence of nitric oxide synthase (NOS) I and NOS II inhibitors. Using the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), neuronal and enteric glial components of NO production were demonstrated. Nicotinic receptors were identified on enteric neurons, which express NOS I, and enteric glia, which express NOS II. These data identify a unique pathway in the mouse colon whereby nicotinic cholinergic signalling in myenteric ganglia mobilizes NO from NOS II in enteric glia, which in coordinated activity with neurons in the myenteric plexus modulates epithelial ion transport, a key component of homeostasis and innate immunity.

Diabetes-related alterations in the enteric nervous system and its microenvironment

“…The EGCs network has trophic and protective functions toward enteric neurons and is fully implicated in the integration and the modulation of neuronal activities [33][34][35] . In addition, EGCs within the ENS have a significant role in forming a diffusion barrier around the capillaries surrounding ganglia similar to that of bloodbrain barrier [3,15,[36][37][38] . Interstitial cells of Cajal (ICCs) are also related to the ENS and are electrically coupled to the smooth muscle cells.…”

“…The secretion of glia cell-derived neurotrophic factor (GDNF), nerve growth factor (NGF) and transforming growth factor-beta contribute to the maintenance of endothelial integrity and vasodilatation [82] . Evidence is accumulating that EGCs share the ability of astrocytes to regulate tight-junction integrity and cellular interactions comparable with those maintaining the blood-brain barrier and creating the proper microenvironment for enteric neurons [36,38] . To know the exact mechanisms of how EGCs contribute to gut homeostasis under physiological and pathophysiological conditions is therefore important to work out new therapeutic strategies and to be aware of diabetes-related vascular complications.…”

Emerging roles for enteric glia in gastrointestinal disorders

“…The presence of cytokine receptors on enteric glia is a very interesting feature of this study and should be confirmed with additional experimental approaches. Enteric glia may also contribute to ileus through the production of NO from iNOS (37,38), though this has yet to be directly demonstrated.…”

Biological applications of the electrochemical sensing of nitric oxide: fundamentals and recent developments

“…The high density of NOS-containing neurons in the young ileum is believed to contribute to this result . Recently, it has been suggested that NO release from neurons and enteric glia can be triggered by nicotinic signaling to regulate epithelial ion transport in segments of mouse colon (MacEachern et al , 2011 ).…”

“…Similarly, modified platinum microelectrodes can also be used (Shin et al , 2008 ;Park et al , 2009 ). Other forms of carbon materials have been investigated, including nanotubes and nanoparticles Porras Gutierrez et al , 2009 ;Deng et al , 2010 ;Xu et al , 2011 ;Chng and Pumera , 2012 ), graphene and nanosheets of graphite (Wu et al , 2010 ;Ng et al , 2011 ;Chng and Pumera , 2012 ), and boron-doped diamond (BDD) electrodes (Patel et al , 2008bMacEachern et al , 2011 ). Microfabrication has also been extensively used to produce NO sensors in the form of microelectrode arrays Chang et al , 2005 ;Patel et al , 2008a ;Trouillon et al , 2010aTrouillon et al , , 2012Quinton et al , 2011 ) or microfluidic systems with integrated electrochemical detection Cha et al , 2010 ;Gunasekara et al , 2012 ).…”