Shape of epithelial cells and intercellular channels in the rabbit proximal nephron.

In electron micrographs of proximal convoluted (PCT) and proximal straight tubules (PST), epithelial height was divided into five zones of equal thickness. Morphometric techniques were used to calculate surface area of cell wall bordering intercellular channels in each zone. Surface concentration of total lateral cell surface is 3.85 mu2/mu3 of PCT and 2.90 mu2/mu3 of PST. For tubules normalized to outer diameter = 40mu and inner diameter = 25mu, total lateral area is 29 X 10(5) mu2/mm of PCT and 22 X 10(5) mu2/mm of PST. Zone 5 adjacent to basement membrane has similar area (congruent to 17 X 10(5) mu2/mm) and fine structure in PCT and PST. However, the luminal four-fifths of the two cells differ markedly. Lateral area in PCT zones 1 through 4 increases approximately exponentially (from 1.1 X 10(5) to 6.4 X 10(5) mu2/mm) and constitutes 44% of total area. Respective areas in PST increase at a rate greater than exponential (from 0.7 X 10(5) to 2.6 X 10(5) mu2/mm) but constitute only 23% of total. From these data and the estimated number of cells per millimeter of tubule (825), circumferences of individual cells were estimated and quantitative three-dimensional cell models were constructed. The shape of intercellular channels is similar to that of the space between concentric, truncated and pleated horns.