Fig. 1.

Effect of luminal (L) and/or basolateral (B) mPKI (5 μM) on basal and flow-stimulated net cation transport in isolated perfused rabbit cortical collecting ducts (CCDs). A: net Na absorption (J_Na) increased in untreated control (C) tubules as the luminal flow rate was increased from 1 to 5 nl·min⁻¹·mm⁻¹. mPKI added to the luminal and/or basolateral solutions had no effect on flow-stimulated J_Na, although the luminal inhibitor modestly increased J_Na in tubules perfused at a slow flow rate. Luminal iberiotoxin (IBX), an inhibitor of BK but not ROMK channels, had no effect on baseline J_Na in tubules perfused with mPKI. B: net K secretion (J_K) increased ∼3-fold in response to a 5-fold increase in luminal flow rate in control CCDs. Addition of mPKI to the luminal but not basolateral solution increased J_K in CCDs perfused at a flow rate of 1 nl·min⁻¹·mm⁻¹; a subsequent increase in flow rate augmented J_K only slightly. Addition of mPKI to the basolateral solution alone or in the presence of luminal inhibitor inhibited flow stimulation of J_K. Luminal IBX completely inhibited the mPKI-mediated increase in J_K observed in CCDs perfused at a flow rate of 1 nl·min⁻¹·mm⁻¹. Values are means ± SE. For each protocol, n is indicated in results. *P < 0.05 compared with J_x at 1 nl·min⁻¹·mm⁻¹ in same tubules. #P < 0.05 compared with J_x in control tubules studied at same flow rate. Δ, P < 0.01 compared with J_K at 1 nl·min⁻¹·mm⁻¹ in the same experimental group.