Aim of the study: Lubricating gut pill (LGP), a traditional Chinese formula, had been conformed to improve the loperamide-induced rat constipation by stimulation of Cl(-) secretion, but its mechanism has not been fully explored. Thus, the purpose of this study was to identify the action sites of LGP-stimulated Cl(-) secretion across rat distal colonic mucosa.
Materials and methods: Rat distal colonic mucosa was mounted in Ussing chambers and short circuit current (I(SC)), apical Cl(-) current and basolateral K(+) current were recorded. Intracellular cyclic adenosine monophosphate (cAMP) content and protein kinase A (PKA) activity were determined with ELISA kit and the non-radioactive PepTag test, respectively.
Results: LGP at 800μg/ml elicited a sustained increase in Cl(-) secretory response, which was inhibited by CFTR(inh)172, a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor. Permeabilizing apical membrane with nystatin revealed that LGP-stimulated basolateral K(+) current was significantly inhibited by KCNQ1 K(+) channel inhibitor chromanol 293B. LGP-stimulated I(SC) was markedly reduced by pretreatment with cis-N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2amine (MDL-12,330A) and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), but not with inhibitors of Ca(2+)-dependent signaling pathway. Treatment of tissue with LGP resulted in an increase in intracellular cAMP level and the activation in protein kinase A. The E-prostanoid(4) (EP)(4) receptor antagonist L-161,982 completely eliminated LGP-induced response.
Conclusions: The results showed that LGP enhances Cl(-) and fluid secretion via prostanoid receptor signaling and also cAMP and protein kinase A pathway, subsequently triggering the activation of apical Cl(-) channels mostly CFTR and basolateral cAMP-dependent K(+) channel.
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