Fig. 1

Inhibition of the swelling-induced chloride current (I _Cl ) and chloride permeability by the antiviral drug azidothymidine (3′-azido-3′-deoxythymidine, AZT) in NIH 3T3 fibroblasts

(a) AZT blocks I_Cl irreversibly. The cells were held at 0 mV and clamped repetitively to a potential of +40 mV for 400 msec (all values given without leak subtraction). Current measurements were taken 1–5 min after drug application. The insert depicts the molecular structure of the compound used. (b) Original tracing showing the inhibitory effect of 100 µM AZT (hypotonic + AZT) on the swelling-induced chloride current (hypotonic) in the same NIH 3T3 fibroblast. Voltage clamp protocol as above. (c) Current voltage relation of the swelling-induced chloride current in the absence (hypotonic; open symbols) and presence of 100 µM AZT (hypotonic + AZT; closed symbols). The cells were held at 0 mV and voltage steps made for 800 msec from −80 mV to +80 mV in 20 mV increments. The current measurements after decreasing extracellular osmolarity are −1466 ± 143 pA, −1053 ± 107 pA, +1692 ± 184 pA, and +4091 ± 404 pA in the absence of AZT, and −367 ± 111 pA, −185 ± 59 pA, +248 ± 76 pA, and +551 ± 170 pA in the presence of AZT at −80 mV, −40 mV, +40 mV, and +80 mV, respectively (for both, n = 5; peak current was measured 10 msec after pulse onset). (d) Measurements of chloride permeability (P_Cl) in NIH 3T3 fibroblasts in the absence (control) and presence of 100 µM AZT (AZT). Independent measurements of eight cells in the absence and nine cells in the presence of AZT are summarized as total percentage of the KSCN-quenchable MEQ signal plotted for a time frame of 30–150 sec after addition of KSCN (% KSCN quenching; see Materials and Methods).