Effects of aldosterone on NEM-sensitive ATPase in rabbit nephron segments

Aldosterone (aldo) treatment of animals stimulates the rate of H+ secretion in the collecting duct, a process which may involve an H+-ATPase sensitive to inhibition by NEM (N-ethylmaleimide). Therefore, we determined NEM-sensitive ATPase activity in distal nephron segments from three groups of adrenalectomized (adx) rabbits maintained on different doses of aldo (in an osmotic minipump) for seven days. Group 1 was given 1.5 micrograms aldo/100 g body wt/day, whereas groups 2 and 3 were maintained on 5 micrograms and 50 micrograms of aldo/100 g body wt/day, respectively. Aldo concentrations in the plasma of groups 1, 2 and 3 were 10.4 +/- 0.8, 70 +/- 7 and 408 +/- 133 ng/dl, respectively. There was a significant increase in NEM-sensitive ATPase activity in connecting tubule (CNT) and cortical, outer and inner medullary duct segments (CCD, OMCD and IMCD) but not in cortical thick ascending limb (CTAL) and distal convoluted tubule (DCT) in group 2 as compared to group 1. A further increase in plasma concentration of aldo (group 3) did not produce any more increase in NEM-sensitive ATPase activity in the CNT, CCD, OMCD and IMCD, but did increase the enzyme activity in the DCT. These results are consistent with the hypothesis that aldo increases H+ secretion in the connecting tubule and collecting duct segments by increasing the activity of NEM-sensitive H+-ATPase activity in these segments.