Fig. 1.

Flow stimulation of net K secretion (left) and Na absorption (right) in the maturing rabbit CCD. Net transport was measured at slow (∼1 nl·min⁻¹·mm⁻¹), moderate (∼2 nl·min⁻¹·mm⁻¹), and fast (∼5 nl·min⁻¹·mm⁻¹) flow rates in tubules isolated from 2-, 4-, and 6-wk-old rabbits (n = 5–6 per age group) and microperfused in vitro. Net K secretion was absent at 2 wk of age and could not be stimulated by an increase in tubular fluid flow rate. Although a 5-fold increase in flow rate stimulated net Na absorption at 4 wk to levels comparable to those observed at 6 wk of age, no flow-induced increase in net K secretion (FIKS) was detected at 1 mo of life in response to an increase in flow rate to 5 nl·min⁻¹·mm⁻¹. Weaning occurs in the rabbit by 4 wk of age. FIKS was clearly evident by 6 wk of age. [Adapted from Satlin (173) and Woda et al. (237).]