Structural and functional study of the rat distal nephron: effects of potassium adaptation and depletion.

To examine the relationship between tubular transport of potassium and cell structure in segments of the superficial distal nephron, we performed potassium transport and quantitative electron microscopic studies in rats after potassium adaptation and potassium depletion. In distal nephrons continuously microperfused in vivo, potassium adaptation stimulated potassium secretion by 200%. Microperfused distal convoluted tubules (earliest portion of accessible distal nephron) did not, however, secrete potassium in potassium adapted animals. Morphometric analysis of the distal convoluted tubule also revealed no detectable effect of potassium diet on the structure of the distal cell type. In contrast, examination of the connecting tubule and the initial collecting tubule of the distal nephron demonstrated a striking increase in basolateral membrane in potassium-adapted animals. This change was limited to the connecting tubule cell and the principal cell type. No structural change of the intercalated cell type in either segment was associated with altered potassium transport. We conclude that cells of the distal convoluted tubule do not secrete potassium. Functional and morphologic evidence suggests that potassium is secreted by the connecting tubule cell and the principal cell of the connecting tubule and the initial collecting tubule, respectively.