ATPase Activity In Segments Research Articles

Influence of age on nitric oxide modulatory action on Na +, K +-ATPase activity through cyclic GMP pathway in proximal rat trachea

Age-related changes in the modulatory action of nitric oxide (NO) on cyclic GMP levels and Na +,K +-ATPase activity in the proximal rat trachea were investigated using sodium nitroprusside, 8-bromo-cyclic GMP and okadaic acid. At 24 months, both control activities of Na +,K +-ATPase and Mg 2+-ATPase were decreased when compared to the segments from 4- and 12-month-old animals. However, cyclic GMP levels were similar among the three ages. Sodium nitroprusside (100 μM) induced stimulation of Na +,K +-ATPase activity in segments from both 4- and 12-month-old animals, but not 24-month-old animals. The effect was specific for Na +,K +-ATPase since Mg 2+-ATPase activity was unaffected. Sodium nitroprusside induced an increase in nitrates/nitrites and cyclic GMP levels in proximal segments at 4, 12 and 24 months. The 8-bromo-cyclic GMP (100 μM) induced a similar specific stimulation of Na +,K +-ATPase activity in segments from 4- and 12- but not 24-month-old animals. Okadaic acid (1 μM), a phosphatase-1 inhibitor, increased proximal Na +,K +-ATPase but not Mg 2+-ATPase activity in tissues from 4-, 12- and 24-month-old animals. Our results suggest that aging affects cyclic GMP pathway in proximal rat trachea by an action at the level of the cyclic GMP-dependent protein kinase.

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.

Measurement of Na K ATPase activity in segments of proximal tubules from superficial and juxtamedullary rat nephrons during antidiuresis.

The role of active sodium transport in the partes rectae of subcortical and juxtamedullary proximal nephrons has not yet been established. Recent knowledge of the histotopographical positions of both types of pars recta has now enabled them to be accurately distinguished and isolated from freeze-dried sections. Na K ATPase activity was measured in single dissected tubular segments by an ultramicro method. No significant difference in Na K ATPase activity in the partes rectae from subcortical and juxtamedullary nephrons could be detected.