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. Ca 2+ 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 Ca 2+ transients and displayed low expression of voltage-dependent Ca 2+ conductances. These are properties of intramuscular ICC (ICC-IM) that cannot regenerate and propagate slow waves. A T-type Ca 2+ channel antagonist had no effect on Ca 2+ transients, but these events were blocked by thapsigargin and CPA, suggesting they result from Ca 2+ release. PS ICC expressed ANO1, a Ca 2+ -activated Cl - conductance. Ca 2+ released from stores actives ANO1 channels, thus exerting a depolarizing influence on PS. Ani9, 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 post-stimulus depolarization and contraction. 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 Ca 2+ transients and activation of ANO1 regulates PS tone and mediates inputs from enteric neurons.