Hits act against residual transport and differ from known PSAC inhibitors.

(A) Osmotic lysis kinetics in PhTMA lysis solution without (black trace) or with 200 μM furosemide (green or red traces). Addition of 0.1, 0.3, or 1 μM PRT-1 (top to bottom red traces, respectively) inhibits residual lysis. (B) Dose responses for inhibition of residual permeability (P) of PhTMA+ or proline (red and blue circles, respectively; mean ± S.E.M. of up to 10 trials each). (C) Inhibitor concentrations that block uptake by 50% (K0.5). Mean ± S.E.M. for inhibition of residual transport in PhTMA+ + 200 μM furosemide or primary transport in sorbitol are shown on a logarithmic scale as black and red bars, respectively. While ISG-21 and TP-52 have higher affinities against primary transport, PRT inhibitors have comparable or greater activity against residual transport. (D) Dose responses for PRT-1 inhibition of residual P in PhTMA+ plus either 100 nM ISG-21 or 2 μM TP-52 (blue and green triangles, respectively; mean ± S.E.M. of up to 3 trials each). Solid lines in panels (B) and (D) represent the best fits to the sum of two Langmuir isotherms [11].