Ontogeny of k+ transport in rat distal colon .
Aizman, R. I., G. Celsi, L. Grahnquist, Z. M. Wang, Y. Finkel, and A.
Aperia.
Dept. of Woman and Child Health, Pediatric Unit, St.
G[diaeresis]oran's Children's Hospital, Karolinska Inst., S-11281,
Stockholm, Sweden
APStracts 3:0017G, 1996.
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.
We have here 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 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, were lower in I than
in A rats. In contrast, the activity of K+-ATPases located in apical
membrane and measured as ouabain-insensititive SCH-28080-sensitive,
as ouabain-sensitive Na+-independent ATP hydrolysis, and as 86Rb
uptake were significantly higher in I than in A rats. The ratio
between apical 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 a mRNA expression
of both ATPases was sig nificantly 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 colon. Conclusion: The relative
activity of apical K+ absorbing ATPases is higher in the I than in
the A colon, which should aid the infants in retaining K+.
Received 24 July 1995; accepted in final form 3 January 1996.
APS Manuscript Number G313-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96