ClC-1 current is similar in FDB fibers before and after formamide detubulation in paired experiments, despite a significant reduction in membrane capacitance. (A) Families of 9-AC–sensitive ClC-1 currents recorded from a representative FDB fiber isolated from a 15-d-old mouse before (black) and after (red) formamide addition and withdrawal. The striking similarity in ClC-1 activity before and after formamide detubulation is emphasized by superimposing the two families of 9-AC–sensitive ClC-1 currents (right). Total cell capacitance for this fiber was reduced from 603 to 352 pF after formamide addition and withdrawal. (B) Average membrane capacitance was significantly reduced 40.6 ± 2% (n = 10) in FDB fibers from 15–16-d-old mice after formamide addition and withdrawal. (C) Average voltage dependence of steady-state ClC-1 currents recorded from FDB fibers from 15–16-d-old mice before (filled symbols) and after (open symbols) formamide addition and withdrawal. Data are presented as mean ± SEM (n = 10 each control and detubulated fibers).