EXPRESSION OF ACID-BASE-RELATED PROTEINS IN MESONEPHRIC KIDNEY OF THERABBIT

The mesonephric kidney, precursor to the metanephric kidney, comprises 30-50 nephrons, each with a glomerulus and proximal, distal, and coll ecting tubules. Although two different cell types have been identified in the mesonephric collecting tubule, no relationship to cells of the metanephric collecting duct has been established. To characterize exp ression of some of the acid-base-related proteins, we assayed for carb onic anhydrase (CA) activity and performed immunocytochemistry in meso nephroi from 15- to 20-day-old fetal rabbits. From total RNA, we detec ted expression of CA II and CA IV mRNA. Microdissected proximal and co llecting tubules abundantly expressed both CA II and CA IV, at least t o the extent observed in mature metanephric proximal tubules and colle cting ducts. Histochemistry confirmed the expression of CA activity in these segments; in the collecting tubule, 28% of the collecting tubul e cells were CA rich. Most CA-rich cells showed apical H+-ATPase and b asolateral band 3 anion exchanger staining consistent with the finding s in mature H+-secreting (alpha) intercalated cells of the metanephric collecting duct. CA-negative cells could be labeled with an antibody that identifies mature metanephric principal cells. Thus the mesonephr ic collecting tubule has many cells resembling mature a-intercalated c ells and a majority of cells resembling principal cells. The similarit y to the metanephric collecting duct suggests that the lineages of met anephric alpha-intercalated and principal cells may be closely related to those of the mesonephros.