Role of interstitial cells of Cajal in neural control of gastrointestinal smooth muscles.

Specialized cells known as interstitial cells of Cajal (ICC) are distributed in specific locations within the tunica muscularis of the gastrointestinal tract and serve as electrical pacemakers, active propagation pathways for slow waves, and mediators of enteric motor neurotransmission. Recent morphological studies have provided evidence that motor neurotransmission in the gut does not occur through loosely defined synaptic structures between nerves and smooth muscle, but rather via synaptic-like contacts that exist between varicose nerve terminals and intramuscular ICC (ICC-IM). ICC-IM are coupled to smooth muscle cells via gap junctions and electrical responses elicited in ICC are conducted to muscle cells. Electrophysiological studies of the stomach of wild-type and mutant animals that lack ICC-IM have provided functional evidence for the importance of ICC in cholinergic and nitrergic motor neurotransmission. The synaptic-like contacts between nerve terminals and ICC-IM facilitate rapid diffusion of transmitters to specific receptors on ICC. ICC-IM also play a role in generating unitary potentials in the stomach that contribute to the excitability of the gastric fundus and antrum.