Insensitivity of TPP currents to MEND. BHK cells using standard solutions with 2 mM ATP and 0.2 mM GTP on the cytoplasmic side. (A) The rapid application of extracellular solution containing 40 µM C12TPP causes an immediate 0.2-nA inward current and a MEND response amounting to 70% of C_m within 15 s. Thereafter, the renewed application of C12TPP generates an inward current of similar magnitude but no further loss of C_m. DSF, 6.6. (B) The rapid application of 10 mM C4TPP induces an inward current of 0.6 nA. After the induction of a 63% MEND response with 200 µM TX100, the C4TPP current is reduced by only 12% on average. DSF, 1,017. (C) Normalized results (n = 5) for the same protocols using 40 µM C12TPP, 0.12 mM C10TPP, 0.25 mM C6TPP, 10 mM C4TPP, and 0.5 mM TtPP. The average MEND responses ranged from 45 to 57%. The average current decrease was 10% for C12TPP, 15% for C10TPP, 26% for C6TPP, 17% for C4TPP, and 31% for TtPP. Slopes of current–voltage relations and average DSP values are given below the bar graphs for each agent.