This study investigated the effect of the anion, SCN-, on the conductive properties of single proximal tubule cells isolated from frog kidney. Ionic currents were measured using the conventional whole-cell patch clamp technique. 2. Addition of SCN- to the bath solution alone had a biphasic effect; there was an initial rapid rise, followed by a slower secondary increase, in both outward and inward conductances. However, when SCN- was added to the bath in the presence of pipette SCN-, such that the concentration gradient for movement of SCN- into the cell was abolished, only the fast changes in conductance were observed. 3. Cells did not discriminate between cations and anions under nominally K(+)-free control conditions. However, in the presence of intracellular SCN- cells became anion selective. Taken together with the increased conductance, this suggests activation of a Cl- channel (gSCN). 4. Niflumic acid, a Cl- channel blocker, inhibited gSCN in a dose-dependent manner, with a half-maximal blocking concentration (Ki) of 28 +/- 2.8 microM and a Hill coefficient of 1.2 +/- 0.3 (n = 6). 5. The activation of gSCN by intracellular SCN- was dose dependent and showed positive co-operativity, with a Ki of 62.3 microM and Hill coefficient of 4.0. 6. Plasma and urine levels of SCN- range between 10 and 70 microM, thus the conductance described here may play a role in the regulation of Cl- handling by the kidney.
