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 CPA, suggesting they result from Ca2+ release.
 PS ICC expressed ANO1, a Ca2+-activated Cl-
conductance.  Ca2+ 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 Ca2+ transients and activation of ANO1 regulates PS
tone and mediates inputs from enteric neurons.