Na, K-ATPase and the development of Na+ transport in rat distal colon

Abstract

Na,K-ATPase function was studied in order to evaluate the mechanism of increased colonic Na+ transport during early postnatal development. The maximum Na(+)-pumping activity that was represented by the equivalent short-circuit current after addition of nystatin (ISCN) did not change during postnatal life or after adrenalectomy performed in 16-day-old rats. ISCN was entirely inhibited by ouabain; the inhibitory constant was 0.1 mM in 10-day-old (young) and 0.4 mM in 90-day-old (adult) rats. The affinity of the Na,K pump for Na+ was higher in young (11 mM) than in adult animals (19 mM). The Na,K-ATPase activity (measured after unmasking of latent activity by treatment with sodium dodecylsulfate) increased during development and was also not influenced by adrenalectomy of 16-day-old rats. The inhibitory constant for ouabain (KI) was not changed during development (0.1-0.3 mM). Specific [3H]ouabain binding to isolated colonocytes increased during development (19 and 82 pmol/mg protein), the dissociation constant (KD) was 8 and 21 microM in young and adult rats, respectively. The Na+ turnover rate per single Na,K pump, which was calculated from ISCN and estimated density of binding sites per cm2 of tissue was 500 in adult and 6400 Na+/min.site in young rats. These data indicate that they very high Na+ transport during early postnatal life reflects an elevated turnover rate and increased affinity for Na+ of a single isoform of the Na,K pump. The development of Na+ extrusion across the basolateral membrane is not directly regulated by corticosteroids.

Correlation of function and structure in developing rat distal colon

“…In agreement with our previous studies the activity of the electrogenic Na + transport pathway and Na, K-ATPase rose during the weaning period (Pácha et al 1991. aSCC increased by more than 105% and Na, K-ATPase activity by 30%.…”

“…Na, K-ATPase activity was measured in crude homogenates of mucosal scrapings by determining the release of inorganic phosphate from ATP as described previously (Pácha et al 1991). Enzyme activity was calculated as the difference between ATPase activity without and with ouabain (2×10 -3 M) and expressed as micromoles of P i per milligram of protein per hour.…”

“…In particular, Na + transport and Na, KATPase activity exhibit considerable ontogenetic changes. In the rat colon, Na, K-ATPase activity reveals an agedependent increase (Pácha et al 1991), although Na + absorption is very high during the suckling period and significantly decreases later (Finkel et al 1988). The very high Na + absorption is predominantly a consequence of electrogenic amiloride-sensitive Na + transport which increases during the suckling period, reaches a peak during weaning and entirely disappears later (Pácha et al 1987.…”

Development of Intestinal Transport Function in Mammals

“…Second, the existence of multiple carbohydrate transporters has been proposed on the basis of kinetic analysis (53, 238), but molecular biological proof is lacking. Third, although developmental changes of the Na ϩ -K ϩ -ATPase turnover number has been reported (295), no information is available for nutrient transporters. As far as glucose absorption is concerned, the lactose in milk is hydrolyzed in the small intestine by lactase into glucose and galactose, and these sugars are absorbed by a Na ϩ -dependent transport pathway (84,162,319,357).…”

Carbenoxolone Accelerates Maturation of Rat Intestine

“…Alkaline phosphatase activity was determined by the method of Murer et al (20) using p-nitrophenol phosphate as substrate, and p-nitrophenol was measured at alkaline pH. The activity of Na,K-ATPase was measured as the ouabainsensitive release of inorganic phosphate from ATP as has been described previously (21). Enzyme activities were calculated as micromoles of reaction product (glucose, p-nitrophenol, phosphate) per milligram of mucosal protein per hour.…”