Characterization of TX100-induced MEND using simultaneous optical and electrical recordings in BHK cells. The pipette solutions contained 2 mM ATP and 0.2 mM GTP. (A) 5 µM FM 4–64 was applied and removed twice, and then 120 µM TX100 was applied for 30 s, inducing a 66% MEND response. FM dye was applied and removed twice more. Membrane binding of FM dye decreases 73% after MEND. (B) 5 µM FM 4–64 was applied once and washed. During the second application, 120 µM TX100 was applied for 30 s, inducing a 65% MEND response. After MEND, FM dye was applied and removed three more times. FM fluorescence remaining in the cell does not wash off and amounts to 70% of pre-MEND fluorescence, corresponding roughly to the amount of membrane internalized as per capacitive measurements.