Chapter 1 - Nerves, smooth muscle cells and interstitial cells in the GI tract: Molecular and cellular interactions

Abstract

Multiple cell types generate and organize the movements of the gut muscles required to process nutrients and wastes in the GI tract. Central to motility are smooth muscle cells (SMCs) that generate the forces necessary to propel luminal contents or restrict movements. SMCs are not capable of organ level cooperation without complex regulatory mechanisms. Unrestrained, SMCs are a detriment to propulsive activity because of their intrinsic but cell-to-cell uncoordinated excitability properties. SMCs are coupled electrically to interstitial cells forming a regulatory unit called the SIP syncytium. SIP is an acronym that describes a syncytium of electrical network cells formed by the SMCs, ICC (Interstitial Cells of Cajal) and PDGFR2+ (Platelet-derived growth factor receptor alpha). Interstitial cells generate electrical rhythmicity and synchronize the contractions of SMCs into phasic contractions. Interstitial cells also receive and transduce neural inputs. Superimposed upon the regulation provided by the SIP syncytium, the enteric nervous system senses the volume and composition of luminal contents through intrinsic primary sensory nerves (IPANs) and generates motility patterns at the whole organ level. These effects are further mediated through 5-hydroxy tryptamine (Serotonin), acetyl choline, vasoactive intestinal peptide, nitric oxide and others. Neuropathies of the enteric nervous system are associated with serious motility disorders.