Regulation of bicarbonate secretion as fluid excretion in the salivary ducts

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In the present study, we investigated the exclusion of fluorescent dye from the duct lumen by carbachol (CCh) in isolated parotid interlobular duct segments to clarify the ability of the ducts for the fluid secretion with bicarbonate secretion. CCh decreased the fluorescent intensity in the duct lumen during the superfusion of the fluorescent dye, and CCh flushed out small viscous substances stained with the fluorescent dye from isolated duct lumen. Methazolamide and removal of external Ca^<2+> suppressed CCh-induced clearance of the duct fluorescence. A major portion was inhibited by removal of bicarbonate in the superfusion solution and DPC, but not low concentration of external CT, bumetanide or DIDS. Patch-clump investigation indicated the presence of Ca^<2+> -activated anion channels, and gramieidin-perforated patched analysis indicated that bicarbonate was a major portion of outward currents in the isolated duct cells. These results suggest that carbachol evoles fluid secretion possibly through Ca^<2+> -activated, DPC-sensitive anion channels with HCO_3^- secretion in the rat parotid intralobular ducts.