Site of the acidification defect in the perfused postobstructed collecting tubule

The effect of prior urinary tract obstruction on total CO2 flux in cortical and medullary collecting tubules was examined using an unilateral ureteral obstruction model and isolated tubule in vitro microperfusion. Tubules were obtained from the control and obstructed kidneys after 1, 2, and 4 days of obstruction. Paired comparison of function of cortical or medullary tubules and urine pH was made. Medullary collecting tubules showed decreased acidification after 2 days of obstruction (7.7 +/- 8.5 vs. 29.9 +/- 6.6 pmol/mm/min). Cortical collecting tubules from the obstructed kidney showed high rates of acidification at all time periods examined, and rates from the postobstructed cortical collecting tubules exceeded levels from control tubules at the 24-hour period while barely missing significance (p less than 0.06) at the 48- and 96-hour periods. These data are not consistent with the hypothesis that the acidification defect in the postobstructed kidney occurs in the cortical collecting tubule by a voltage-dependent mechanism.