Maturation of chloride-bicarbonate exchange in rat ileal brush border membrane vesicles

Brian D. Riedel, Fayez K. Ghishan

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

The present studies were designed to examine the ontogeny of the ClHC03 exchange process in the ileum of suckling (2 wk old), weanling (3 wk old), and adult (6 wk old) rats using well-validated brush border membrane vesicle techniques. The purity of the vesicle preparation was verified by demonstrating that the activity of brush border marker enzyme activity was enriched 30-fold compared to the cell homogenate. Glucose uptake experiments demonstrated an overshoot phenomenon under Na+ gradient conditions, but not in the absence of Na+. Chloride uptake varied inversely with the extravesicular osmolarity, demonstrating that transport was into an os-motically sensitive space. Membrane binding accounted for only 20% of total uptake. An inwardly-directed pH gradient (pHout/pHi„ = 5.2/7.5) produced overshoot Cl uptake in all age groups. The magnitude of overshoot was greatest in suckling rats and declined with advancing age. Addition of an outwardly-directed HCO3- gradient yielded further stimulation of CI" uptake in suckling and weanling animals but could not be demonstrated in the adult. The majority of Cl uptake proceeded via an electroneutral exchange process. However, a conductive component was present, as demonstrated by enhancement of uptake when the vesicles were rendered positive inside by a K+ gradient and valino-mycin, as compared with voltage clamp conditions. At 5 mM concentration, 4,4'-diisothiocyanostilbene-2,2'-disul-fonic acid, an inhibitor of anion exchange, inhibited Cl uptake by 62, 44, and 33%, respectively in suckling, weanling, and adult rats. The initial rate of uptake was linear for 8 s. Kinetic studies at 5 s demonstrated a Km for 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive Cl uptake of 21.4 ± 10.7,11.5 ± 7.6, and 7.9 ± 8.3 mM, and Vmax of 72.9 ± 14.4, 19.5 ± 3.7 and 4.5 ± 1.1 nmol/mg protein/min in the suckling, weanling, and adult periods respectively (mean ± SEM). These studies demonstrate for the first time the presence of a Cr-HCC3 exchanger in the suckling rat ileum, which declines in activity with advancing age.

Original languageEnglish (US)
Pages (from-to)189-193
Number of pages5
JournalPediatric Research
Volume25
Issue number2
DOIs
StatePublished - Feb 1989
Externally publishedYes

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health

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