Potassium transport across the intestines of the fowl Gallus domesticus

Abstract

1. We investigated potassium (K) transport in vitro across four major segments of the avian intestine. In normal fed birds, the most proximal segment, the duodenum, had very low unidirectional rates of K transport (Jms 6.7 nEq·cm−2·hr−1; Jsm 7.7 nEq·cm−2·hr−1). The jejunum had the greatest unidirectional K flux of the segments studied (Jms 36.6 and Jsm 85.5 nEq·cm−2·hr−1), and this segment showed a net K secretion (48.9 nEq·cm−2·hr−1). The ileum had a significantly lower Jms (16.5 nEq·cm−2·hr−1) than did the jejunum, and this segment also showed a net K secretion (28 nEq·cm−2·hr−1). Potassium transport across the mucosal surface of the colon was very low (Jms 7.7 nEq·cm−2·hr−1) while the Jsm flux was relatively large, giving a net K secretion of 45.7 nEq·cm−2·hr−1. 2. When tissues were bathed in solutions having approximately normal in vivo K concentrations on both sides of the membranes and open circuit PD (to simulate in vivo conditions), the jejunum was the only segment that showed a net K absorption (83 nEq·cm−2·hr−1). 3. When birds were fed a low K diet for 2 weeks, the colon showed the greatest response with Jms for K increasing 12 fold over control. 4. From these studies we conclude that in normal birds the duodenum appears to be relatively impermeable to K and does not appear to play a significant role in K transport. However, the jejunum by virtue of its relatively greater permeability to K, the total length of jejunum comprising the intestine (66%), and the in vivo K gradients, seems to be most important in K absorption in the normal bird. The ileum and colon were major sites of K secretion in vitro and appear to be most important in intestinal regulation of K transport in response to changes in the dietary K load.