Movement of Solutes across Luminal Cell Membranes in Kidney Tubules of the Rabbit

Abstract

SLICES of kidney cortex have been used to advantage in the investigation of the mechanism of renal transport systems¹, although the technique has definite limitations. Thus it could be calculated that the contribution of the membrane which separates the cell from the tubular lumen (luminal membrane) to the turnover of paramino hippurate in slices is negligible². Similarly, the luminal membrane appears to play no part in the turnover of potassium in slices³; only the peritubular membrane seems to be involved here. Among possible reasons for this is the length of the path of diffusion through the convoluted tubule and/or the collapse of the tubular lumen as a result of continued reabsorption of salt and water⁴. The influence of the length of the tubule is seen, for example, in a preparation of teased flounder kidney. In this case, efflux of dyes from the lumen is dependent on energy⁵, which suggests that the path of efflux lies across the cell and that there is little loss of dye directly from the lumen to the medium.