Figure 3. Inwardly rectifying K⁺ currents in 60 mm external K⁺.

A–D, inwardly rectifying currents were recorded in 60 mm external K⁺ from voltage-clamped neonatal myocytes isolated from wild-type, Kir2.1^−/−, Kir2.2^−/− and Kir2.1^−/−-Kir.2.2^−/− mice. For each family of current traces, the voltage was stepped from a holding potential of −10 mV to potentials of −10 to −70 mV (in 15 mV increments). Leak currents were subtracted using currents evoked by small depolarizing pulses (P/4 method). Cell capacitances were 15, 14, 11 and 15 pF, respectively. E, steady state currents (means ±s.e.m.) were plotted as a function of voltage in wild-type (n = 4), Kir2.1^−/− (n = 8), Kir2.2^−/− (n = 11) and Kir2.1^−/−-Kir.2.2^−/− (n = 9) myocytes. Current amplitudes were measured at the end of the 500 ms voltage-clamp step and were normalized to cell capacitance to control for cell surface area.