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Ontogeny of K+ transport in rat distal colon
R I Aizman1, G Celsi, L Grahnquist
1Department of Woman and Child Health, St. Göran's Children's Hospital, Karolinska Institute, Stockholm, Sweden.
Insights
Infants require higher potassium retention than adults for growth. This study reveals that infant colons enhance potassium absorption via increased activity of apical potassium-transporting ATPases, aiding potassium retention.
Area of Science:
- Physiology
- Developmental Biology
- Gastroenterology
Background:
- Infants have higher potassium (K+) requirements than adults to prevent growth retardation.
- Colonic potassium transport is crucial for maintaining K+ homeostasis.
- Developmental differences in K+ regulation mechanisms are expected between infants and adults.
Purpose of the Study:
- To investigate the developmental changes in colonic potassium transport pathways.
- To compare the activity and expression of various K+-transporting ATPases in infant and adult rat colons.
- To elucidate the mechanisms underlying enhanced K+ retention in infants.
Main Methods:
- In vivo colonic perfusion studies in infant (I) and adult (A) rats.
- 86Rubidium (86Rb) uptake assays to measure K+ transport.
- Measurement of vanadate-sensitive P-type ATPases, Na(+)-K(+)-ATPase, and apical K(+)-ATPases activity.
- Northern blot analysis to determine alpha-mRNA expression of H(+)-K(+)-ATPase and Na(+)-K(+)-ATPase.
Main Results:
- Net colonic K+ uptake was significantly higher in infant rats compared to adults.
- While ~80% of 86Rb uptake was vanadate-sensitive in both groups, the contribution of specific ATPases differed.
- Infant colons exhibited lower Na(+)-K(+)-ATPase activity but significantly higher activity of apical K(+)-ATPases (ouabain-insensitive, SCH-28080-sensitive).
- Alpha-mRNA expression for both H(+)-K(+)-ATPase and Na(+)-K(+)-ATPase was higher in infant rats.
- The ratio of apical K(+)-ATPases to basolateral Na(+)-K(+)-ATPase activity was 3.2-fold higher in infant colons.
Conclusions:
- The infant colon possesses a higher relative activity of apical K+ absorbing ATPases compared to adults.
- These developmental adaptations in colonic K+ transport facilitate enhanced potassium retention in infants.
- This mechanism is vital for meeting the increased K+ demands during infant growth.
Abstract:
Infants need to retain more K+ than adults to avoid growth retardation. Since the K+ requirements are different in infants (I) and in adults (A), the mechanisms regulating K+ homeostasis should also be different. The colon plays an important role for the regulation of K+ homeostasis. Colonic K+ transport is bidirectional. In this study we have examined the development of colonic K+ transport with special reference to the contribution of different K(+)-transporting pathways. The net colonic K+ uptake, as determined by in vivo perfusion studies and by 86Rb uptake, was significantly higher in I than in A rats. In both I and A colon, approximately 80% of total 86Rb uptake was dependent on vanadate-sensitive P-type adenosinetriphosphatases (ATPases), but the contribution of these different ATPases changes during development. The activity of colonic Na(+)-K(+)-ATPase, measured as ouabain-sensitive Na(+)-dependent ATP hydrolysis and as 86Rb uptake, was lower in I than in A rats. In contrast, the activity of K(+)-ATPases located in apical membrane and measured as ouabain insensitive and SCH-28080 sensitive, as ouabain-sensitive Na(+)-independent ATP hydrolysis, and as 86Rb uptake was significantly higher in I than in A rats. The ratio between apically located K(+)-ATPases and basolateral Na(+)-K(+)-ATPase activities was almost 3.2-fold higher in I than in A colon. We identified with Northern blot the expression of the colonic H(+)-K(+)-ATPase and the Na(+)-K(+)-ATPase alpha-subunits. The alpha-mRNA expression of both ATPases was significantly higher in I than in A rats. The pH and K+ sensitivity of the ouabain-insensitive, SCH-28080-sensitive K(+)-ATPase was the same in I and A colons. In conclusion, the relative activity of apical K+ absorbing ATPases is higher in the I than in the A colon, which should aid infants in retaining K+.