Abstract
Interstitial cells of Cajal (ICC) regulate smooth muscle excitability and motility in the gastrointestinal (GI) tract. ICC in the deep muscular plexus (ICC-DMP) of the small intestine are aligned closely with varicosities of enteric motor neurons and thought to transduce neural responses. ICC-DMP generate Ca(2+) transients that activate Ca(2+) activated Cl(-) channels and generate electrophysiological responses. We tested the hypothesis that excitatory neurotransmitters regulate Ca(2+) transients in ICC-DMP as a means of regulating intestinal muscles. High-resolution confocal microscopy was used to image Ca(2+) transients in ICC-DMP within murine small intestinal muscles with cell-specific expression of GCaMP3. Intrinsic nerves were stimulated by electrical field stimulation (EFS). ICC-DMP exhibited ongoing Ca(2+) transients before stimuli were applied. EFS caused initial suppression of Ca(2+) transients, followed by escape during sustained stimulation, and large increases in Ca(2+) transients after cessation of stimulation. Basal Ca(2+) activity and the excitatory phases of Ca(2+) responses to EFS were inhibited by atropine and neurokinin 1 receptor (NK1) antagonists, but not by NK2 receptor antagonists. Exogenous ACh and substance P (SP) increased Ca(2+) transients, atropine and NK1 antagonists decreased Ca(2+) transients. Neurokinins appear to be released spontaneously (tonic excitation) in small intestinal muscles and are the dominant excitatory neurotransmitters. Subcellular regulation of Ca(2+) release events in ICC-DMP may be a means by which excitatory neurotransmission organizes intestinal motility patterns.