Figure 4. Inward Ba²⁺ currents in wild-type and Kir2.1^−/− neonatal ventricular myocytes.

A and B, Ba²⁺ currents through T- and L-type Ca²⁺ channels were recorded in the presence of external TTX and internal Cs⁺ from voltage-clamped neonatal myocytes isolated from wild-type and Kir2.1^−/− mice. For each family of current traces, the voltage was stepped from a holding potential of −80 mV to potentials of −40 to +50 mV (in 15 mV increments). Cell capacitances were 17 and 16 pF, respectively. C, steady state currents (means ±s.e.m.) were plotted as a function of voltage in wild-type (n = 9) and Kir2.1^−/− (n = 9) myocytes, with and without the addition of 1 μm nifedipine to reduce L-type currents. Currents were measured 50 ms into the voltage pulse and were normalized to cell capacitance to control for cell surface area.