Fig. 5.
Both PD307243 and NS1643 worked from outside the cell membrane, yet their effects were independent of each other. A, left, time course of changes in hERG current amplitude expressed in a COS-7 cell M), and total before, during, and after bath application of PD (PDo, 10 μ current suppression by dofetilide (DOF). Currents were elicited by the voltage-clamp protocol diagrammed on top of the right panel. Current amplitudes were measured from the peak of tail current at −60 mV and normalized by the control right before PD application. The time course of onset of PD effect was fit with a single exponential function with τ value of 6 min. Right, superimposed current traces from the same experiment at time points a, b, and c. B and C, left, time course of changes in hERG current amplitude expressed in oocytes before and after intraoocyte drug injection (estimated cytoplasmic concentrations denoted: PDi, ~ 300 μM; and NSi, ~1000 μM), during exposure to drugs applied to the bath solution (PDo, 10 μM; NSo, 30 μM) and after intraoocyte injection of TEA (TEAi, ~ 2 mM). In each experiment, the same injecting pipette was used first for PD or NS injection and then for TEA injection. Right, superimposed current traces from the same experiments as in left at the specified time points. Inset of right in B, percentage increase in hERG current amplitude caused by 10 μM PD tested in COS-7 cells and in oocytes measured from the peak amplitudes of outward tail currents at −60 mV (66 ± 10 and 61 ± 8, n = 4 and 20, p > 0.05). The same conclusion could be reached by measuring time-dependent test pulse currents at +40 mV: PD increased the current by 187 ± 67% and 185 ± 16% in COS-7 cells and in oocytes, respectively. D, left, time course of changes in hERG current amplitude before and during bath application of 20 μM PD and after adding NS 30 μM in the continuous presence of PD. Right, percentage increase in current amplitude caused by NS in the absence (−PD) or presence of PD (+PD).