Postnatal maturation of inwardly rectifying potassium current in isolated ventricular myocytes

We have used the whole-cell voltage-clamp method to study the inwardly rectifying potassium channel in ventricular myocytes isolated from neonatal (N, < 3 days), infant (I, 10-17 days) and mature (M, > 3 months) rabbits. Currents were elicited by serial hyper- and de-polarization from a holding potential of -80 mV in the presence and absence of barium chloride (2 mM). Barium-sensitive currents, which showed properties of inward rectification and a reverse potential at -80 to -70 mV, actually reflected currents through inwardly rectifying potassium channels. The current-voltage relations and inward rectification occurring over the range of -50 to -10 mV were relatively similar in the three groups. However, the slope conductance of Ikl decreased and the extent of inward rectification increased with maturation. The slope conductance of Ikl was 3.45 +/- 0.42 nS/pF (n = 8) for N myocytes, 2.72 +/- 0.45 nS/pF (n = 11) for I myocytes and 1.28 +/- 0.19 nS/pF (n = 8) for M myocytes (p < 0.05 among the three groups and between each group). The greater slope conductance of Ikl is important in maintaining the electrical stability in smaller immature cells with larger axial resistance. The age-related changes of Ikl may contribute to the progressive lengthening of the action potential of myocytes. In summary, the present study has identified the maturation-associated changes of Ikl which are characterized by a decrease in slope conductance and an increase in the extent of inward rectification which can in part explain the transition of action potential characteristics.(ABSTRACT TRUNCATED AT 400 WORDS)