Regulation of anion transport across the uterine epithelium ofGallus domesticus

Abstract

For egg shell production, cations, primarily Ca(2+), and anions, primarily HCO(3)(-), must be secreted across the uterine epithelium. Because alterations of HCO(3)(-) transport influence Ca(2+) secretion, the present study was performed to gain insight into the regulation of anion transport (i.e., chloride and HCO(3)(-) transport) across the egg shell gland of the domestic chicken. To this purpose, unstripped uterus epithelia were mounted in modified Ussing chambers and electrogenic [i.e., short circuit current (I(sc))] and electroneutral anion transport were measured. Stimulating adenylate cyclases by forskolin, thereby enhancing the intracellular cyclic adenosine monophosphate( )(cAMP) concentration, evoked 2 patterns of I(sc) responses. Under HCO(3)(-)-buffered conditions, some of the tissues (3/8) showed an increase of I(sc), whereas in others (5/8) a decrease of I(sc) was observed in the presence of the drug. The I(sc) increase existed in HCO(3)(-) secretion because under HCO(3)(-)-free conditions forskolin stimulated only an I(sc) decrease. In addition, methazolamide, a blocker of carboanhydrases, significantly reduced baseline I(sc). The forskolin-induced decrease of I(sc) presented a Cl(-) absorption. In the absence of HCO(3)(-), forskolin yielded only an I(sc) decrease and the transepithelial flux of (36)Cl(-) was reduced. In the presence of mucosal 5-nitro-2-(3-phenylpropylamino) benzoic acid, a nonselective blocker of chloride channels, forskolin-induced I(sc) decrease was inhibited. In addition to cAMP, the regulatory influence of neurons or prostaglandins on baseline I(sc) and anion transport was investigated. Neither tetrodotoxin, a blocker of neuronal Na(+) conductances, electrical field stimulation, nor indomethacin, a blocker of cyclooxygenases, influenced the baseline I(sc) or anion transport. In summary, these data show effects of forskolin (i.e., cAMP) on anion transport across the egg shell gland of the domestic chicken: HCO(3)(-) secretion (supporting Ca(2+) mineralizing of the egg shell) and Cl(-) absorption. Neurons or prostaglandins did not influence the anion transport.