Possible epithelial sodium channels visualized by freeze-fracture.
The coprodeum is a very efficient Na+-retaining epithelium. Coprodeum from birds on a high Na+ diet has virtually no ion transport, while an Amiloride-sensitive Na+ absorption of 10--12 mu equiv . cm-2 . h-1 is induced in the coprodeal epithelium from birds on a low Na+ diet. Both measurements of the Na+ influx and Na+-diffusion potentials across the luminal cell membrane have revealed a selective opening of this membrane to Na+ in birds on a low Na+ diet. Freeze-fracture P faces of the luminal membrane in coprodea taken from birds on a low Na+ diet have rod-shaped particles, 100 x 240 A, in more than 20% of the principal cells. Rod-shaped particles appear in less than 1% of these cells in coprodea from high Na+-diet birds. Thus a low Na+ diet induces rod-shaped particles in the luminal cell membrane of the hen coprodeum. These new particles may function as Na+-channels mediating the increased Na+-influx across the apical cell membrane.
D000818:Animals; D001717:Birds; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002988:Cloaca / Q000648:ultrastructure*; D004039:Diet, Sodium-Restricted; D004848:Epithelium / Q000648:ultrastructure; D005260:Female; D005614:Freeze Fracturing; D007473:Ion Channels / Q000648:ultrastructure*; D012964:Sodium / Q000378:metabolism
D007473:Ion Channels; D012964:Sodium