In situ studies of distal convoluted tubule in rat. II. K secretion

Microperfusion and free-flow micropuncture studies were performed in anesthetized rats to compare the rates of K flux in early and late segments of the distal tubule. Early distal segments were located within the initial 40% of distal tubule length, and late distal segments were located within the terminal 35% of the distal tubule. In early distal segments of control rats, significant K secretion was observed at perfusion rates of 6 and 14 nl/min. In high-K rats significant K secretion was only observed at the lower perfusion rate. Late segments of control rats secreted 70.5 +/- 8.2 at the low flow rate and 139 +/- 18.9 pmol X min-1 X mm-1 at the high flow rate. In K-adapted rats, values were 134.4 +/- 30.2 and 178 +/- 29.3 pmol X min-1 X mm-1. During free flow, we observed a K flux in control rats of 11.0 +/- 9.4 pmol X min-1 X mm-1 (NS) in early segments and a K flux of 55 +/- 6.5 pmol X min-1 X mm-1 in late segments. In K-adapted rats, values were 18.3 +/- 6.7 (P less than 0.05) in early and 123 +/- 17.2 pmol X min-1 X mm-1 in late segments. The majority of our data suggests that the distal convoluted tubule secretes K at a low rate that is not influenced by flow rate or a high-K diet.