John Malysz

Interstitial cells of Cajal direct normal propulsive contractile activity in the mouse small intestine

BACKGROUND & AIMS Interstitial cells of Cajal (ICC) have been linked to the generation of intestinal pacemaker activity, but their role in in vivo motor dysfunction is unclear. In this study, we investigated the hypothesis that ICC play a role in the generation of distention-induced peristalsis using W/Wv mice that lack ICC associated with Auerbachs plexus. METHODS Radiological observations were made of the movement of contrast fluid through the proximal small intestine. Electrical activities were recorded in the external muscle layers. In addition, intraluminal pressure changes were recorded in isolated intestinal segments. RESULTS In control mice, after gavage of 0.5 mL of barium sulfate in the stomach, the contrast fluid moved through the proximal small intestine in peristaltic waves at approximately 47 times a minute, propagating aborally at approximately 2 cm/s. Electrical slow waves and intraluminal pressure waves were synchronized at similar frequencies and propagation velocities. In W/Wv mice, such regular peristaltic waves were not observed. Action potentials and contractions appeared random, and contents moved back and forth in an irregular manner. The net propulsive effect of contractile activity in W/Wv mutant mice was much weaker than that in controls. CONCLUSIONS Slow wave controlled peristalsis occurs in the normal proximal small intestine upon gastric emptying of a semiliquid. This motor pattern is absent in W/Wv mice that lack ICC.

Developmental origin and Kit-dependent development of the interstitial cells of Cajal in the mammalian small intestine

Interstitial cells of Cajal (ICCs) form a network of cells between the external longitudinal and circular muscle layers at the level of the Auerbachs plexus in the mammalian small intestine. These cells express the Kit receptor tyrosine kinase and are essential for intestinal pacemaker activity. W mutant mice carrying structural mutations in the Kit gene lack both the network of ICCs and intestinal pacemaker activity. We were interested in the developmental origin of the cells that make up the network of ICCs. In addition, the specific stages of ICC development that require a functional Kit receptor have not been characterized. We show that ICCs originate from mesenchymal progenitor cells that coexpress both Kit and smooth muscle myosin heavy chain, a marker specific for smooth muscle, during embryogenesis. ICC and longitudinal smooth muscle lineages begin to diverge late in gestation. Embryos homozygous for the regulatory Wbanded (Wbd) mutation do not express Kit in these mesenchymal progenitor cells. Nevertheless, Wbd/Wbd mice display a normal network of ICCs and normal smooth muscle layers at postnatal day 5 (p5). Adult Wbd/Wbd mice lack a functional ICC network and intestinal pacemaker activity due to a failure of the ICCs to increase in numbers after p5.  These data suggest a common developmental origin of the ICCs and the longitudinal smooth muscle layers in the mammalian small intestine and show that Kit expression is necessary for the postnatal development and proliferation of ICCs but not for the initial cell lineage decision toward an ICC fate during embryogenesis or for smooth muscle development. Dev. Dyn. 1998;211:60‐71.

Pinaverium acts as L-type calcium channel blocker on smooth muscle of colon.

The effect of pinaverium was electrophysiologically characterized and compared with the established L-type calcium channel blockers diltiazem, D600, and nitrendipine on canine colonic circular smooth muscle. Effects were studied on the electrical activity of the smooth muscle cells, in particular the spontaneously occurring slow wave. In addition, effects were examined on spontaneous contraction patterns and contractile activities generated by stimulation of cholinergic nerves or directly by stimulating muscarinic receptors. Effects were also examined on excitation of NO-releasing intrinsic nerves. Pinaverium bromide affected the slow wave by selectively inhibiting the plateau potential that is associated with generation of contractile activity. Pinaverium, similar to diltiazem and D600, produced reductions in cholinergic responses as well as spontaneous contractions. The IC50 values for inhibition of cholinergic responses for pinaverium, diltiazem, and D600 were 1.0 x 10(-6), 4.1 x 10(-7), and 5.3 x 10(-7) M, respectively. The IC50 values for inhibition of spontaneous contractile activity for pinaverium, diltiazem, and D600 were 3.8 x 10(-6), 9.7 x 10(-7), and 8.0 x 10(-7) M, respectively. Increases in contractility by carbachol were abolished by pretreatment with either pinaverium or D600. In addition, neither pinaverium nor D600 had any effects on the inhibitory NO-mediated relaxations. These data provide a rationale for the use of pinaverium in the treatment of colonic motor disorders where excessive contraction has to be suppressed.

Searching for intrinsic properties and functions of interstitial cells of Cajal.

Evidence is mounting that interstitial cells of Cajal may function as pacemaker cells and have a role in NO-mediated neurotransmission. Several colonic motor disorders may be associated with abnormal ICC function.

385 Conditional Genomic Deletion of Ano1 in Kit-Expressing Cells of Adult Mice Results in Loss of Slow Waves and Reduced Coordination of Ca2+ Transients in Myenteric Interstitial Cells of Cajal of the Small Intestine

In the enteric nervous system (ENS), glia outnumber neurons by 4 to 6-fold and form an extensive network throughout the gastrointestinal tract. Enteric glia are essential for normal gastrointestinal function and play roles in regulating epithelial barrier integrity, epithelial cell proliferation and neuronal support. While glial subtypes can be clearly distinguished in the central and peripheral nervous systems (CNS and PNS), it remains unknown whether similar glial diversity exists in the ENS. Because of their morphology and expression of Glial Fibrillary Acidic Protein (GFAP), until recently, enteric glia were thought to resemble astrocytes. We tested the hypothesis that enteric glia instead constitute a unique and heterogeneous group of glial cells. To define the level of heterogeneity, we first analyzed expression of the markers S100β, Sox10, GFAP, and proteolipid protein 1 (PLP1) in the small and large intestine of adult mice. Sox10 and S100β are widely expressed by enteric glia throughout the intestine. GFAP expression, however, is more restricted. Marker expression in combination with cellular location reproducibly distinguished subpopulations of enteric glia, suggesting that functional subtypes are likely to exist. Unexpectedly, we found that PLP1 is widely expressed by enteric glia, although they do not myelinate axons. We then performed RNA sequencing analysis (RNA-Seq) on PLP1-expressing cells in the mouse intestine and compared their gene expression to that of other types of glia in the CNS and PNS. This showed that enteric glia are transcriptionally distinct from other glial classes, and share the greatest similarity to myelinating glia. The gene expression database generated by this study will facilitate future studies of glial function in gastrointestinal physiology.