Ri. Aizman et al., ONTOGENY OF K+ TRANSPORT IN RAT DISTAL COLON, American journal of physiology: Gastrointestinal and liver physiology, 34(2), 1996, pp. 268-274
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 differen
t. The colon plays an important role for the regulation of K+ homeosta
sis. Colonic K+ transport is bidirectional. In this study we have exam
ined the development of colonic K+ transport with special reference to
the contribution of different K+-transporting pathways. The net colon
ic K+ uptake, as determined by in vivo perfusion studies and by Rb-86
uptake, was significantly higher in I than in A rats. In both I and A
colon, similar to 80% of total Rb-86 uptake was dependent on vanadate-
sensitive P-type adenosinetriphosphatases (ATPases), but the contribut
ion of these different ATPases changes during development. The activit
y of colonic Na+-K+-ATPase, measured as ouabain-sensitive Na+-dependen
t ATP hydrolysis and as Rb-86 uptake, was lower in I than in A rats. I
n contrast, the activity of K+-ATPases located in apical membrane and
measured as ouabain insensitive and SCH-28080 sensitive, as ouabain-se
nsitive Na+-independent ATP hydrolysis, and as Rb-86 uptake was signif
icantly higher in I than in A rats. The ratio between apically located
K+-ATPases and basolateral Na+-K+-ATPase activities was almost 3.2-fo
ld higher in I than in A colon. We identified with Northern blot the e
xpression of the colonic H+-K+-ATPase and the Na+-K+-ATPase a-subunits
. The alpha-mRNA expression of both ATPases was significantly higher i
n I than in A rats. The pH and K+ sensitivity of the ouabain-insensiti
ve, SCH-28080-sensitive K+-ATPase was the same in I and A colons. In c
onclusion, the relative activity of apical K+ absorbing ATPases is hig
her in the I than in the A colon, which should aid infants in retainin
g K+.