COMPARISON OF I-TO IN YOUNG AND ADULT HUMAN ATRIAL MYOCYTES - EVIDENCE FOR DEVELOPMENTAL-CHANGES

In an effort to understand the tonic basis for the developmental chang es that have been reported to occur in the configuration of the human atrial action potential, we characterized the transient outward curren t (I-to) and the inward rectifier current in atrial myocytes isolated from 20 young (ages 1 day-2.5 yr) and 8 adult (11-68 yr) human hearts using the whole cell patch-clamp technique. We found evidence for stat istically significant(P < 0.05) age-related changes in the I-to, inclu ding 1) the presence of an I-to in only 67% of the cells isolated from young hearts vs. 100% of the cells isolated from adult hearts, 2) an almost twofold increase in the current density of I-to in adult cells vs. young cells, and 3) recovery kinetics that are approximately twofo ld slower in young myocytes relative to adult myocytes. In contrast, t here were no age-related changes found in the current density of the i nward rectifier current or the sustained current measured after the de cay of I-to. These results suggest important current-dependent changes that occur with age in human atria.