Does the ostrich ( Struthio camelus) coprodeum have the electrophysiological properties and microstructure of other birds?

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The ostrich is unique among birds in having complete separation of urine and faeces. The coprodeal epithelium is thus during dehydration exposed to a fluid 500 mOsm hyperosmotic to plasma. We have investigated whether the coprodeum is adapted like a mammalian bladder. The coprodeal epithelium was studied by electrophysiology in the Ussing chamber, and the anatomy by light microscopy and scanning electron microscopy. Electrophysiology: The short-circuit current (SCC) and open circuit electrical potential difference were recorded. The change induced by 0.1 mmol mucosal amiloride was recorded. An average basal SCC of 162±29 μA/cm 2 was observed, and a resistance of 297±34 Ω cm 2 calculated. These values are as observed in other avian coprodea. The resistance is much lower than in mammalian bladders (10 000 Ω cm 2). The amiloride-sensitive SCC, equal to net sodium absorption, was approximately 5 μmol/cm 2 h as observed in other avian species. Anatomy: The mucosal membrane is composed of broad irregular folds with very short intestinal glands containing an unusually high proportion of goblet cells. Conclusion: The ostrich coprodeum is not adapted like a mammalian bladder. The abundance of goblet cells results in a copious secretion of mucus that establishes a thick unstirred layer giving effective osmotic protection.