ULTRACYTOCHEMICAL STUDY OF THE PATHWAY OF CA2-CELL LAYER OF A NEPHRON( TRANSPORTATION ACROSS THE EPITHELIAL)

The pathway of Ca2+ absorption across the renal epithelial layer was u ltracytochemically investigated in nephrons using an oxalate-pyroantim onate technique. Reaction products were strongly detected in the inter cellular space in proximal tubules, and in intracellular organelles in distal tubules in the cortex and the outer layer of the outer medulla . These findings are suggestive of paracellular transport of Ca2+ in t he proximal tubule, and transcellular transport in the distal tubule. The transcellular pathway of Ca2+ is of interest, as intracellular Ca2 + concentrations must be maintained. Ca-precipitates, in the distal tu bule cells, were detected en masse in mitochondria, and to a lesser ex tent, in smooth endoplasmic reticulum, Golgi apparatus and vesicles. P recipitates were rare in lysosomes and rough endoplasmic reticulum. Ca lcium containing organelles distributed throughout the cytoplasm. Free precipitates in the cytoplasmic matrix were only rarely seen in the a pical portion of the cells. It seems that Ca2+ immediately after enter ing a cell, binds to calcium binding proteins, or is sequestered to or ganelles like mitochondria, Golgi apparatus, smooth endoplasmic reticu lum or vesicles. In this way, fluctuations in intracellular Ca2+ conce ntrations are avoided. These organelles may be involved in Ca-transpor t in Ca-absorbing cells.