Regulation of anion transport across the uterine epithelium of Gallus domesticus
2011
Brockmeier, K. | Schultheiss, G.
For egg shell production, cations, primarily Ca²⁺, and anions, primarily HCO₃⁻, must be secreted across the uterine epithelium. Because alterations of HCO₃⁻ transport influence Ca²⁺ secretion, the present study was performed to gain insight into the regulation of anion transport (i.e., chloride and HCO₃⁻ 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 (Isc)] and electroneutral anion transport were measured. Stimulating adenylate cyclases by forskolin, thereby enhancing the intracellular cyclic adenosine monophosphate (cAMP) concentration, evoked 2 patterns of Isc responses. Under HCO₃⁻-buffered conditions, some of the tissues (3/8) showed an increase of Isc, whereas in others (5/8) a decrease of Isc was observed in the presence of the drug. The Isc increase existed in HCO₃⁻ secretion because under HCO₃⁻-free conditions forskolin stimulated only an Isc decrease. In addition, methazolamide, a blocker of carboanhydrases, significantly reduced baseline Isc. The forskolin-induced decrease of Isc presented a Cl⁻ absorption. In the absence of HCO₃⁻, forskolin yielded only an Isc decrease and the transepithelial flux of ³⁶Cl⁻ was reduced. In the presence of mucosal 5-nitro-2-(3-phenylpropylamino) benzoic acid, a nonselective blocker of chloride channels, forskolin-induced Isc decrease was inhibited. In addition to cAMP, the regulatory influence of neurons or prostaglandins on baseline Isc 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 Isc 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: HCO₃⁻ secretion (supporting Ca²⁺ mineralizing of the egg shell) and Cl⁻ absorption. Neurons or prostaglandins did not influence the anion transport.
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