Fig. 5.

Effect of luminal (L) and/or basolateral (B) calphostin C (500 nM) on flow-stimulated net cation transport in isolated perfused rabbit CCDs. A: J_Na increased in untreated control (C) tubules as the luminal flow rate was increased from ∼1 to 5 nl·min⁻¹·mm⁻¹. Calphostin C added to the luminal but not bilateral solutions modestly inhibited the magnitude of flow-stimulated J_Na. Luminal IBX had no effect on baseline J_Na in tubules perfused with calphostin C. B: J_K increased ∼3-fold in response to a 5-fold increase in luminal flow rate in control CCDs. Addition of calphostin C 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 failed to augment J_K further. Addition of calphostin C to both luminal and basolateral solutions had the same effect as addition of the inhibitor to the luminal solution alone. Luminal IBX completely inhibited the increase in J_K observed in CCDs perfused with calphostin C and studied 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 and @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.