Electrical properties of pig colonic mucosa measured during early post‐natal development.

Abstract

Microvillar membrane (Vm) and transmural (Vt) potential differences were measured in proximal colon taken from pigs at birth and up to 10 days of age. Vm remained independent of the age of the animal provided it was measured in the absence of methionine. The over-all mean was -43.3 mV. Adding methionine to fluid bathing the mucosal surface of newborn pig colon caused a 9.8 mV depolarization of Vm and a 6.7 mV increase in Vt. These effects, which were Na+-dependent, were not seen in the 10 day old animal. Substituting SO42- for Cl- in methionine-free medium caused a hyperpolarization in Vm. Increasing the concentration of K+ caused corresponding depolarization. Substituting choline for Na+ had no effect on Vm. Cl- and K+ movement across the microvillar membrane together account for the bulk of the measured membrane potential. These results applied to all stages of development. Na+ uptake across the microvillar membrane of the newborn pig colon was increased in the presence of methionine. This effect disappeared in older animals. Na+ uptake in the absence of methionine doubled during the first 24 h of post-natal life. This increase was maintained using colons taken from older animals. Methionine depolarization of Vm in the newborn pig colon was probably caused by the electrogenic influx of Na+. The ability of the colon to actively concentrate methionine within its mucosa disappeared at the same time as methionine ceased to affect Vm and Vt. Methionine and Na+ formed a ternary complex with a carrier in the brush border of the newborn pig colon. This carrier was lost or modified during early post-natal development.