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Figure 4 Membrane currents of a hyperthyroid (A) and a control (B) pulmonary vein (PV) cardiomyocyte. The ionic currents were elicited on depolarization from –40 mV to +60 mV. The inset shows the various clamp protocols. The hyperthyroid and control PV cardiomyocytes had similar electrical capacitance. C and D show the measured current-voltage curves of the two cells. The overall transient outward (I_to) and the steady state outward currents (I_k) were indicated by circles and triangles, respectively.