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The structural relationships between interstitial cells of Cajal (ICC), varicose nerve fibers, and smooth muscle cells in the gastrointestinal tract have led to the suggestion that ICC may be involved in or mediate enteric neurotransmission. We characterized the distribution of ICC in the murine stomach and found two distinct classes on the basis of morphology and immunoreactivity to antibodies against c-Kit receptors. ICC with multiple processes formed a network in the myenteric plexus region from corpus to pylorus. Spindle-shaped ICC were found within the circular and longitudinal muscle layers (IC-IM) throughout the stomach. The density of these cells was greatest in the proximal stomach. IC-IM ran along nerve fibers and were closely associated with nerve terminals and adjacent smooth muscle cells. IC-IM failed to develop in mice with mutations in c-kit. Therefore, we used W/WV mutants to test whether IC-IM mediate neural inputs in muscles of the gastric fundus. The distribution of inhibitory nerves in the stomachs of c-kit mutants was normal, but NO-dependent inhibitory neuroregulation was greatly reduced. Smooth muscle tissues of W/Wv mutants relaxed in response to exogenous sodium nitroprusside, but the membrane potential effects of sodium nitroprusside were attenuated. These data suggest that IC-IM play a critical serial role in NO-dependent neurotransmission: the cellular mechanism(s) responsible for transducing NO into electrical responses may be expressed in IC-IM. Loss of these cells causes loss of electrical responsiveness and greatly reduces responses to nitrergic nerve stimulation.Ramon y Cajal observed cells at the terminus of the autonomic nervous system in the acini of salivary glands, in the connective tissue of the pancreas, between the glands of Lieberkuhn, in the intestinal villi, and within the tunica muscularis of the gastrointestinal (GI) tract (1). The processes of cells in the GI tract, which became known as interstitial cells of Cajal (ICC), form a network that is intercalated between nerve terminals and effector cells. Cajal believed that the structures he identified were essential elements in peripheral neurotransmission (2), and this hypothesis has been investigated for the past century (3). ICC were later recognized to be nonneural (4), but their anatomical locations in the GI tract continue to suggest a role for these cells in neurotransmission (3,5 Recently, it was shown that mutations in c-kit, a protooncogene located at the W locus on chromosome 5 in the mouse that encodes a receptor tyrosine kinase (10), or in stem cell factor, the natural ligand for c-Kit receptors, result in developmental defects in some classes of . For example, ICC in the myenteric plexus region (IC-MY) of the small intestine are greatly decreased in numbers in these mutants and slow waves are abolished, confirming a role for IC-MY as pacemakers (3,15,16). ICC in the region of the deep muscular plexus, however, were unaffected by defects in the c-Kit signaling pathway (14). Loss of IC-MY did not af...

▪ Abstract  In the gastrointestinal tract, phasic contractions are caused by electrical activity termed slow waves. Slow waves are generated and actively propagated by interstitial cells of Cajal (ICC). The initiation of pacemaker activity in the ICC is caused by release of Ca2+ from inositol 1,4,5-trisphosphate (IP3) receptor–operated stores, uptake of Ca2+ into mitochondria, and the development of unitary currents. Summation of unitary currents causes depolarization and activation of a dihydropyridine-resistant Ca2+ conductance that entrains pacemaker activity in a network of ICC, resulting in the active propagation of slow waves. Slow wave frequency is regulated by a variety of physiological agonists and conditions, and shifts in pacemaker dominance can occur in response to both neural and nonneural inputs. Loss of ICC in many human motility disorders suggests exciting new hypotheses for the etiology of these disorders.

Interstitial cells of Cajal (ICC) are interposed between enteric neurons and smooth muscle cells in gastrointestinal muscles. The role of intramuscular ICC (IC-IM) in mediating enteric excitatory neural inputs was studied using gastric fundus muscles of wild-type animals and W/W v mutant mice, which lack IC-IM. Excitatory motor neurons, labeled with antibodies to vesicular acetylcholine transporter or substance-P, were closely associated with IC-IM. Immunocytochemistry showed close contacts between enteric neurons and IC-IM. IC-IM also formed gap junctions with smooth muscle cells. Electrical field stimulation yielded fast excitatory junction potentials in the smooth muscle that were blocked by atropine. Neural responses were greatly reduced in muscles of W/W v animals. Loss of cholinergic responses in W/W v muscles seemed to be caused by the loss of close synaptic contacts between motor neurons and IC-IM, because these muscles were not less responsive to exogenous acetylcholine than were wild-type muscles. W/W v muscles also responded to excitatory nerve stimulation when the breakdown of acetylcholine was blocked by neostigmine. The density of cholinergic nerve bundles within the muscles was not significantly different in wild-type and W/W v muscles, and similar amounts of 14 [C]choline were released from preloaded wildtype and W/W v muscles in response to nerve stimulation. The impact of losing IC-IM on gastric compliance was also evaluated in intact stomachs. Pressure increased as a function of fluid volume and infusion rate in wild-type animals, but W/W v animals showed little basal tone and minimal increases in pressure with fluid infusions. These data suggest that IC-IM play a major role in receiving cholinergic excitatory inputs from the enteric nervous system in the murine fundus.