Separation of proximal tubule cells from suspensions of rat kidney cells in density gradients of Ficoll in tissue culture medium.

Rat kidneys were disaggregated with 0.25% trypsin. Cell were separated by velocity sedimentation in a previously described isokinetic gradient, by isopycnic sedimentation, and by velocity sedimentation followed by isopycnic sedimetation. In some fractions from the isokinetic gradient, 71.8+/-2.4+ of the nucleated cells contained histochemically demonstrable alkaline phosphatase (HDAP); in semithin sections, 62.7+/-2.3% of these cells had brush borders. The correspondence between fractions enriched for cells with HDAP and fractions enriched for brush border suggested that HDAP might be a suitable marker for rat proximal tubule cells. These cell constituted 46.5+/-2.6% of the nucleated cells in the starting sample suspension of kidney cells, and 81.9+/-2.7% of nucleated cells in the purified fractions from the gradients. More than 98% of nucleated cells in these fractions excluded typan blue. Following isopycnin centrifugation, the purest fractions contained 87.3+/-1.5% nucleated cells with HDAP, 9.6+/-2.5% nucleated cells iwithout HDAP, and 3.1+/-2.5% red blood cells. These proximal tubule cells had densities of 1.036 to 1.052 g/ml. With rate-zonal separation followed by isopycnic separation, the purest gradient fraction contained 93.0+/-1.9% nucleated cell with HDAP, 6.0+/-2.3% nucleated cells with HDAP, and 1.0+/-0.9% red blood cells. These proximal tubule cells sedimented a density of 1.041 g/ml. More than 98% of these cells excluded trypan blue.