Oxalate transport by proximal tubule of the rabbit kidney.

Oxalate transport was examined in isolated perfused segments of the proximal tubule of the rabbit. When oxalate was present in a concentration of 10(-5) M in the bathing and perfusing solutions, there was a net secretory flux of oxalate of 36.4 +/- 1.4, 34.7 +/- 4.3, and 20.7 +/- 2.8 x 10(-15) mol . min-1 . mm-1 in the superficial S1, S2, and S3 segments, respectively, at a bath temperature of 37 degrees C. The net secretory flux of oxalate in the juxtamedullary S1 and S2 segments was 12.8 +/- 2.5 and 12.5 +/- 3.6 x 10(-15) mol . min-1 . mm-1, respectively. Cooling to 25 degrees C resulted in a significant decrease in the net flux of oxalate. When oxalate was present in the bathing solution only (10(-5) M), the bath-to-lumen flux of oxalate was not different from the net flux in the superficial and juxtamedullary S2 segments. These studies demonstrate that oxalate undergoes net secretion in the rabbit proximal tubule. This occurs against an electrical gradient, in the absence of concentration gradients, and can be inhibited by cooling, suggesting an active transport process. There is significant internephronal heterogeneity in the proximal tubule for oxalate secretion.