Ano1 In Intramuscular Interstitial Cells Of Cajal Plays A Key Role In The Generation Of Slow Waves And Tone In The Internal Anal Sphincter

The mechanism underlying tone generation in the internal anal sphincter (IAS) is controversial. We examined the hypothesis that tone depends upon generation of electrical slow waves (SWs) initiated in intramuscular interstitial cells of Cajal (ICC-IM) by activation of Ca2+-activated Cl(-)channels (encoded by Ano1) and voltage-dependent L-type Ca2+ channels (encoded by Cacna1c). Phasic contractions and tone in the IAS were nearly abolished by ANO1 and Cav(L) antagonists. ANO1 antagonists also abolished SWs as well as transient depolarizations that persisted after addition of Cav(L) antagonists. Tone development in the IAS did not require stretch of muscles, and the sensitivity of contraction to ANO1 antagonists was the same in stretched versus un-stretchedmuscles. ANO1 expression was examined in wildtype and Ano1(/+ egfp) mice with immunohistochemical techniques. Dual labelling revealed that ANO1 expression could be resolved in ICC but not smooth muscle cells (SMCs) in the IAS and rectum. Ano1, Cacna1c and Kit gene expression were the same in extracts of IAS and rectummuscles. In IAS cells isolated with fluorescence-activated cell sorting, Ano1 expression was 26.5-fold greater in ICC than in SMCs while Cacna1c expressionwas only 2-fold greater in SMCs than in ICC. These data support a central role for ANO1 and Cav(L) in the generation of SWs and tone in the IAS. ICC-IM are the probable cellular candidate for ANO1 currents and SW generation. We propose that ANO1 and Cav(L) collaborate to generate SWs in ICC-IM followed by conduction to adjacent SMCs where phasic calcium entry through Cav(L) sums to produce tone.