Figure 5.
Electrophysiological characteristics of large-conductance anion channels recorded from PC12 cells transfected with two VDAC-1 cDNAs. (A) Current fluctuations in an excised, inside-out membrane patch from PC12 cells transfected with mt-VDAC-1–myc cDNA at a holding potential of −25 mV by using symmetrical (138 mM NaCl) internal and external solution (Left). i, current. The all-points histogram (Right) constructed for the entire recording duration, which is shown, in part, at Left, shows two peaks; the peak at 25.3 pA represents basal current with all the channels closed, and the other, at 33.5 pA, shows the main open state of one single channel. (B) Current versus voltage (i–V) relationship obtained for single channels from excised, inside-out patches of PC12 cells transfected with cDNAs encoding mt-VDAC-1 (open circles) and pl-VDAC-1 (closed circles). Each point in the graph is the mean current amplitude between the open and the closed state at a given potential fitted by a Gaussian distribution with pclamp6 software. (C) Voltage dependence of the probability of the channel being in the open state (Popen) obtained for pl-VDAC-1 (closed circles) and mt-VDAC-1 (open circles) transfectants. Popen was calculated from the time the channel spent in the open state compared with the total time (1 min) of the recording at a given voltage. The curves were fitted as the sum of two Boltzmann equations of the form Popen = 1/{1 + e[(Vm−V0)/A]}, where Popen is the probability of finding the channel in the open state at a giving holding potential (Vm), A is the slope factor corresponding to the voltage-sensitivity of the activation, and V0 is the voltage producing half-maximal open probability. The fitted values of V0 are shown in the graph.