Figure 4.

Panel A: Representative currents recorded from a 2 week-old neonate ventricular myocyte in the absence and presence of 100 μM BaCl₂. Currents were elicited by stepping the voltage from the holding potential (−80 mV) to membrane potentials between −110 and −20 mV.Panel B: I-V relation for I_K1 measured in normal conditions ([K⁺]_o, 4.0 mM) as the Ba²⁺-sensitive difference current. Raising [K⁺]_o to 10 mM resulted in an increase in I_K1 and a crossing-over of the I-V relationships. Panel C: I_K1 density in adult midmyocardial cells was less than that seen in neonate ventricular cells.