Ca2+ transients in myenteric glial cells during the colonic migrating motor complex in the isolated murine large intestine

Enteric glia cells (EGCs) form a dense network around myenteric neurons in a ganglia and are likely to have not only a supportive role but may also regulate or be regulated by neural activity. Our aims were to determine if EGCs are activated during the colonic migrating motor complex (CMMC) in the isolated murine colon. Strips of longitudinal muscle were removed and Ca2+ imaging (Fluo-4) used to study activity in EGCs within myenteric ganglia during CMMCs, followed by post hoc S100 staining to reveal EGCs. The cell bodies of EGCs and their processes formed caps and halos, respectively, around some neighbouring myenteric neurons. Some EGCs (36%), which were largely quiescent between CMMCs, exhibited prolonged tetrodotoxin (TTX; 1 mu M)-sensitive Ca2+ transients that peaked similar to 39 s following amucosal stimulus that generated the CMMC, and often outlasted the CMMC (duration similar to 23 s). Ca2+ transients in EGCs often varied in duration within a ganglion; however, the duration of these transients was closely matched by activity in closely apposed nerve varicosities, suggesting EGCs were not only innervated but the effective innervation was localized. Furthermore, all EGCs, even those that were quiescent, responded with robust Ca2+ transients to KCl, caffeine, nicotine, substance P and GR 64349 (an NK2 agonist), suggesting they were adequately loaded with indicator and that some EGCs may be inhibited by substances released by neighbouring neurons. Intracellular Ca2+ waves were visualised propagating between closely apposed glia and from glial cell processes to the soma (velocity 12 mu ms(-1)) where they produced an accumulative rise in Ca2+, suggesting that the soma acts as an integrator of Ca2+ activity. In conclusion, Ca2+ transients in EGCs occur secondary to nerve activity; their activation is driven by intrinsic excitatory nerve pathways that generate the CMMC.