Fig. 4. Effects of the thiol-specific reducing agent 1,4-dithiothreitol (DTT) and of the thiol-specific oxidant 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB) on L-type Ca2+currents (ICa,L). ( A ) Effects of DTT (2 mm, n = 6) on ICa,Las measured at various holding potentials (Vh). ( B ) Effects of DTT (2 mm, n = 5) in the presence of isoflurane. Control values were obtained before addition of isoflurane (1 minimum alveolar concentration). ( C ) Effects of DTNB (original traces from one experiment). After obtaining a control value for ICa,L( trace 1 ), DTNB (200 μm) was added and trace 2 was recorded. Traces 3 and 4 were recorded immediately after washout of DTNB and 4 min later, during which the cells were continuously superfused with control solution. ( D ) Current–voltage relation of ICa,Lbefore, during, and after application of DTNB (200 μm, n = 10).