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Development of solute transport in rabbit proximal tubule. III. Na-K-ATPase activity
Insights
Bicarbonate and glucose transport in infant rabbit kidneys mature rapidly between weeks 4-6, driven by increasing Na-K-ATPase activity. This enzyme reaches adult levels by week 7, supporting near-mature transport functions.
Area of Science:
- Nephrology
- Renal Physiology
- Developmental Biology
Background:
- Early juxtamedullary proximal convoluted tubule transport of bicarbonate (HCO-3) and glucose is significantly lower in infant rabbits compared to adults.
- This developmental pattern suggests a critical role for the Na+-extruding pump, Na-K-ATPase, in mediating these transport processes.
Purpose of the Study:
- To investigate the developmental profile of Na-K-ATPase activity in infant rabbit proximal convoluted tubules.
- To correlate the maturation of Na-K-ATPase activity with the development of HCO-3 and glucose transport.
Main Methods:
- Isolated early juxtamedullary proximal convoluted tubules from infant rabbits (1-7 weeks old) and adult rabbits.
- Kinetic microassay to measure Na-K-ATPase activity (coupled to ATP hydrolysis and NADH oxidation).
- Measurement of ouabain-insensitive ATPase on the same tubular segments.
Main Results:
- Na-K-ATPase activity in the 1st week of life was one-third of adult levels.
- Enzyme activity gradually increased to 60% of adult levels by week 6.
- Na-K-ATPase activity reached adult levels by the 7th week of life.
Conclusions:
- The maturation of HCO-3 and glucose transport in infant rabbit proximal tubules is closely linked to the developmental increase in Na-K-ATPase activity.
- Na-K-ATPase activity reaches adult levels by the 7th postnatal week, coinciding with near-mature transport function.
Abstract:
HCO-3 transport (JHCO-3) in early juxtamedullary proximal convoluted tubules isolated from infant rabbits during the 1st 3 wk of life is about one-third that in tubules obtained from adults. A rapid increase in transport ensues during wk 4 through 6, so that near-mature levels are attained by the end of this time. Because the pattern for development of glucose absorption was similar and because both HCO-3 and glucose absorption are driven by the lumen-to-cell Na+ flux, the activity of Na-K-ATPase (the Na+-extruding pump) was considered to be a critical mediator. A kinetic microassay (which couples ATP hydrolysis to NADH oxidation) allowed the measurement of Na-K-ATPase and ouabain-insensitive ATPase on the same tubular segment. Three to nine early juxtamedullary proximal convoluted tubules were obtained after collagenase treatment of the kidney and four to six rabbits were studied at each week of life. The mean activity of Na-K-ATPase during the 1st wk of life was 44.5 +/- 3.5 pmol X min-1 X mm-1, one-third of the adult level. During an interim period of development (2-6 wk), enzyme activity gradually reached 60% of adult levels (76.3 +/- 3.0 at 6 wk), while transport of HCO-3 and glucose, studied previously in other animals, attained mature rates. Only in the 7th wk did the enzyme activity reach that of the adult (106.8 +/- 6.8 in wk 7 vs. 128.4 +/- 14.0 in adult rabbits).(ABSTRACT TRUNCATED AT 250 WORDS)