Measurement of Na K ATPase activity in segments of proximal tubules from superficial and juxtamedullary rat nephrons during antidiuresis.

The role of active sodium transport in the partes rectae of subcortical and juxtamedullary proximal nephrons has not yet been established. Recent knowledge of the histotopographical positions of both types of pars recta has now enabled them to be accurately distinguished and isolated from freeze-dried sections. Na K ATPase activity was measured in single dissected tubular segments by an ultramicro method. No significant difference in Na K ATPase activity in the partes rectae from subcortical and juxtamedullary nephrons could be detected.