| Abstrakt: |
The internal anal sphincter (IAS) functions to maintain continence. Previous studies utilizing mice with cell-specific expression of GCaMP6f revealed two distinct subtypes of intramuscular interstitial cells of Cajal (ICC-IM) with differing Ca 2+ activities in the IAS. The present study further examined Ca 2+ activity in ICC-IM and its modulation by inhibitory neurotransmission. The spatiotemporal properties of Ca 2+ transients in Type II ICC-IM mimicked those of smooth muscle cells (SMCs), indicating their joint participation in the "SIP" syncytium. Electrical field stimulation (EFS; atropine present) abolished localized and whole cell Ca 2+ transients in Type I and II ICC-IM. The purinergic antagonist MRS2500 did not abolish EFS responses in either cell type, whereas the nitric oxide synthase (NOS) inhibitor N G -nitro-l-arginine (l-NNA) abolished responses in Type I but not Type II ICC-IM. Combined antagonists abolished EFS responses in Type II ICC-IM. In both ICC-IM subtypes, the ability of EFS to inhibit Ca 2+ release was abolished by l-NNA but not MRS2500, suggesting that the nitrergic pathway directly inhibits ICC-IM by blocking Ca 2+ release from intracellular stores. Since inositol (1,4,5)-trisphosphate receptor-associated cGMP kinase substrate I (IRAG1) is expressed in ICC-IM, it is possible that it participates in the inhibition of Ca 2+ release by nitric oxide. Platelet-derived growth factor receptor α (PDGFRα) + cells but not ICC-IM expressed P2Y 1 receptors (P2Y 1 R) and small-conductance Ca 2+ -activated K + channels (SK3), suggesting that the purinergic pathway indirectly blocks whole cell Ca 2+ transients in Type II ICC-IM via PDGFRα + cells. This study provides the first direct evidence for functional coupling between inhibitory motor neurons and ICC-IM subtypes in the IAS, with contractile inhibition ultimately dependent upon electrical coupling between SMCs, ICC, and PDGFRα + cells via the SIP syncytium. NEW & NOTEWORTHY Two intramuscular interstitial cells of Cajal (ICC-IM) subtypes exist within the internal anal sphincter (IAS). This study provides the first evidence for direct coupling between nitrergic motor neurons and both ICC-IM subtypes as well as indirect coupling between purinergic inputs and Type II ICC-IM. The spatiotemporal properties of whole cell Ca 2+ transients in Type II ICC-IM mimic those of smooth muscle cells (SMCs), suggesting that ICC-IM modulate the activity of SMCs via their joint participation in a SIP syncytium (SMCs, ICC, and PDGFRα + cells). |
