Electrogenic sodium transport in the developing rabbit cecum

The adult rabbit cecum absorbs Na by an electrogenic, Cl-independent process that is inhibited by the amiloride analogue phenamil. In the colon, this transport system is unique to the cecum. Because the developing colon exhibits many specialized functions, we have now examined the development of electrogenic Na transport in the newborn rabbit. Cecal tissue from animals between 7 and 38 days old was mounted in modified Ussing chambers for measurement of Na and Cl flux (J) and the short-circuit current (Isc). At 7-10 days, the (Isc) was only 0.8 +/- 0.18 microEq cm-2 h-1, but by 35-38 days it had increased to 4.6 +/- 0.79 microEq cm-2 h-1. The Na transport increased in parallel with Isc; JNanet = -0.49 +/- 0.33 microEq cm-2 h-1 at 7-10 and 4.7 +/- 1.6 microEq cm-2 h-1 at 35-38 days. The Na transport was not inhibited by phenamil (10-4 M) at 7-10 days, but by the 35-38-day period, phenamil reduced the JNanet to 1.6 +/- 0.37 microEq cm-2 h-1. The Cl secretion was not stimulated by theophylline in the 14-16-day-old cecum, nor was Na absorption stimulated by epinephrine. The rabbit cecum does not demonstrate electrogenic Na absorption until after the 4th week of life.