Structural and functional comparison of mesonephric and metanephric proximal tubules

Mesonephric kidneys of the mid-gestation fetus and metanephric kidneys of the adult are known to differ in many gross features but to be qualitatively similar in their cellular morphology. In the present studies, quantitative morphometric and in vitro microperfusion procedures were used to examine further the physical and transport properties of mesonephric and metanephric (S2) proximal tubule segments from rabbit. In perfused mesonephric proximal tubules the volume transport rate was 0.91 +/- 0.08 nl/min per mm tubule length, 2.7 +/- 0.2 nl/min per mm2 basement membrane (outer tubule) surface area, and 0.19 +/- 0.03 nl/min per mm2 basolateral cell membrane surface areas. For comparison, the S2 portion of metanephric proximal tubules is reported to transport 0.33 +/- 0.02 to 0.53 +/- 0.01 nl/min per mm length or, based on the present findings, 2.8 +/- 0.2 to 4.4 +/- 0.8 nl/min per mm2 basement membrane area and 0.16 +/- 0.02 to 0.25 +/- 0.07 nl/min per mm2 basolateral membrane area. Thus, proximal mesonephric and S2 metanephric segments exhibit approximately the same transport per unit area of basement membrane and per unit area of the basolateral cell membranes across which active transport presumably occurs.