Inward rectifier and delayed outward potassium currents in isolated guinea-pig ventricular myocytes: maturation and its role in repolarization.

In accord with previous reports, we have found that action potentials triggered from isolated mature (> 1 month) guinea-pig ventricular myocytes showed a longer duration than those from the neonate (< 1 day). A whole-cell voltage-clamp technique has been used to identify the postnatal changes of inward rectifier (Ikl) and delayed outward potassium currents (Ik), which may be related to the action potential transition. Our results have shown that the degree of maturation of the neonatal guinea-pig is much advanced, as compared to neonatal rabbits and rats. Slope conductance (1230 +/- 110 pS/pF, n = 10, for neonatal, and 1450 +/- 450 pS/pF, n = 10, for mature guinea-pig, p > 0.05) and the inward rectification occurring over a potential range from -50 to -10 mV were relatively similar between the neonatal and mature guinea-pig myocytes. But, the slope conductance of Ik was significantly greater in neonatal (702 +/- 80 pS/pF, n = 10) guinea-pig myocytes than in the mature (194 +/- 23 pS/pF, n = 10, p < 0.01). Therefore, we suggest that (1) the maturation of Ik appears later than that of Ikl, (2) age-related decrease of the slope conductance of Ik could contribute to an age-related lengthening of the action potential duration.