Figure 4. Biophysical characterization defines TcCat as an inward rectifier channel.

A. Representative current traces applying a voltage-step protocol from −80 to 80 mV in 20 mV steps. The recordings were obtained under symmetrical conditions in the absence of Mg²⁺ with bath and pipette solution containing 140 mMKCl, 10 mMHepes-K, pH 7.4. B. Current-voltage relationship under symmetrical conditions described in (A). Data correspond to the unitary currentsrecorded in continuous voltage steps at the indicated holding potentials in the absence (open circles, n = 14) or in the presence of 1 mM MgCl₂ in the bath solution (solid squares, n = 13). The non-linear relationship indicates the inward rectification. C. Current traces obtained at the indicated holding potentials showing the functional association of TcCat in clusters under asymmetrical conditions with bath solution 300 mMKCl and pipette solution 140 mMKCl, both containing 10 mMHepes-K, pH 7.4. Doted lines indicate the open state of the two channels (O₁ and O₂) present in the seal. C indicates the closed state of the channels. Histograms represent the unitary current corresponding to one or 2 channels at the indicated voltages. D. Open probability analysis of the single channel events. Values correspond to mean ± SEM from 14 independent experiments.