Role of interstitial cells of Cajal in regulating tone and responses to enteric motor neurons in the murine pyloric sphincter

Gastric slow waves fail to propagate through the pyloric sphincter (PS), thus isolating the specialized motility patterns of the stomach and small intestine. We investigated the role of interstitial cells of Cajal (ICC) in PS of mice. Ca²⁺ waves in ICC, events responsible for electrical slow waves, propagated along the gastric wall but failed to propagate into the PS. ICC in PS fired localized Ca²⁺ transients and displayed low expression of voltage-dependent Ca²⁺ conductances. These are properties of intramuscular ICC (ICC-IM) that cannot regenerate and propagate slow waves. A T-type Ca²⁺ channel antagonist had no effect on Ca²⁺ transients, but these events were blocked by thapsigargin and cyclopiazonic acid, suggesting that they result from Ca²⁺ release. PS ICC expressed ANO1, a Ca²⁺-activated Cl^- conductance. Ca²⁺ released from stores activates ANO1 channels, thus exerting a depolarizing influence on PS. Ani9, a selective antagonist of ANO1 channels, hyperpolarized cells and reduced contractile tone. Electrical field stimulation (EFS) of intrinsic neurons yielded inhibitory junction potentials (IJPs), and cessation of EFS resulted in poststimulus depolarization and contraction. <i>N</i>^ω-nitro-l-arginine (L-NNA) abolished relaxation responses to EFS and switched responses to contractions. Application of atropine or Ani9 (in the presence of L-NNA) abolished contraction during EFS. Our results describe new and fundamental functions of ICC-IM in the PS. The inability of these cells to propagate slow waves provides the insulator function of PS muscles and localized Ca²⁺ transients, and activation of ANO1 regulates PS tone and mediates inputs from enteric neurons.<b>NEW & NOTEWORTHY</b> The pyloric sphincter is an electrical insulator between the stomach and small intestine, isolating and maintaining the unique motility patterns of these organs. Using Ca²⁺ imaging techniques, this study demonstrates why slow waves do not propagate between organs and how interstitial cells of Cajal serve to regulate pyloric tone and responses to enteric motor neurons.