Differences in epithelial morphology correlate to Na+-transport: A study of the proximal, mid, and distal regions of the coprodeum from hens on high and low NaCl diet

A study was performed to correlate regional morphology and amiloride inhibi table Na+-transport in the coprodeal epithelium in hens, Gallus domesticus, on low-NaCl diet and in controls. Proximal (close to colon), mid and dista l (close to urodeum) regions were examined using light microscopy, transmis sion- and scanning electron microscopy. Na+-transport was measured electrop hysiologically in Ussing-chambers in the proximal and distal regions. The epithelium, simple and columnar, is composed of absorptive intestinal e pithelial cells, goblet cells, brush cells, migrating lymphoid cells, and e nteroendocrine cells. Brush cells, identified in avians for the first time, occur in highest number in the proximal part of the coprodeum in low-NaCl hens. Na+-transport is high in the low-NaCl hens, ranging from 347 mu A/cm( 2) (proximal) to 187 mu A/cm(2) (distal). In control hens, which correspond to hens on high-NaCl diet, it is low in all regions (0-4 mu A/cm(2)). Abso rptive intestinal epithelial cells as well as brush cells adapt to variatio ns in transepithelial Na+-transport by regulating height and packing densit y of their microvilli, number, size, and localization of apical vesicles, a nd the width of the intercellular space. Regional differences in the epithe lial cell composition and ultrastructure are closely correlated to transepi thelial Na+-transport but only in low-NaCl hens, as controls do not show th ese variations. (C) 1999 Wiley-Liss, Inc.