Amiloride-sensitive sodium transport of the rat distal colon during early postnatal development

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Abstract
To evaluate developmental changes in colonic sodium transport, the sensitivity of the transepithelial potential and short-circuit current to amiloride was investigated. The amiloride-sensitive short-circuit current (I sc Na ), which represents the electrogenic sodium transport through Na+ channels, rose significantly from day 5, reached a peak on day 10, and entirely disappeared after weaning. The maximum rate of electrogenic, amiloride-sensitive sodium transport was 12.0 μEq/cm2 · h. TheI sc Na was suppressed by adrenalectomy and/or premature weaning but not by a mineralocorticoid antagonist, spironolactone. On the contrary, treatments which increase aldosterone levels in vivo (low-sodium diet, furosemide-induced natriuresis, high dietary intake of potassium) stimulated theI sc Na . The effect of adrenalectomy increased during postnatal development. The sensitivity ofI sc Na to aldosterone was highest at the end of the weaning period. High-sodium diet, which causes a decrease in circulating aldosterone, was associated with a partial inhibition ofI sc Na (P<0.016). These data suggest that the distal colon of neonatal rats can transport sodium via an electrogenic, amiloride-sensitive mechanism and that adrenocortical hormones exert the main regulatory control of this pathway.