Developmental changes in neurally mediated ion transport in piglet distal colon.

To better understand the role of enteric nerves in the regulation of colonic ion transport in neonates, we examined the effects of endogenous and exogenous neurotransmitters on ion transport across distal colonic tissues of piglets. Tissues were obtained from full-term fetuses; newborns; suckling piglets killed 1 d, 5 d, and 14 d after birth; and 21-d-old piglets that had been weaned for 2 d. Colonic tissues were stripped of external muscle layers and mounted in Ussing flux chambers. Short-circuit current (Isc), a measure of active ion transport, and transmural potential difference were lowest in fetal colons and increased during postnatal development. Tissue conductance remained constant throughout development until d 14 and then rose sharply after weaning. Blockade of enteric neural transmission with tetrodotoxin reduced basal Isc compared with control tissues in fetal, newborn, and 1-d-old piglets but had no effect in older animals. The Na(+)-channel blocker amiloride had no effect on basal Isc in fetal tissues but significantly reduced Isc in all other groups, with the effect increasing with age. Isc responses to electrical field stimulation of enteric neurons were similar in fetal through 14-d-old piglets and then increased after weaning. Increases in Isc after serosal additions of carbachol (10 microM), serotonin (10 microM), or norepinephrine (10 microM) in fetal and newborn piglets were as great or greater than in the older piglets. For serotonin and norepinephrine, Isc responses rose sharply immediately after weaning. In 1-d-old piglets, Isc responses to all stimuli were reduced significantly by removal of Cl- ions from the bathing solutions.(ABSTRACT TRUNCATED AT 250 WORDS)