Developmental changes in long-opening behavior of L-type Ca2+ channels in embryonic chick heart cells.

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Abstract
In the early (3-day) stage of development, long-lasting openings of the L-type Ca2+ channels (mode 2) occur in embryonic chick heart cells. Since mode-2 behavior is infrequently observed in adult heart cells of other species, in the present study, developmental change in behavior of the Ca2+ channel was examined in young (3-day) and old (17-day) embryonic chick heart cells. In the whole-cell voltage clamp, the L-type Ca2+ current carried by Ca2+ ions was smaller in amplitude and had a faster inactivation in 17-day cells than in 3-day cells. The peak current density was 8.1 +/- 0.2 microA/cm2 (mean +/- SEM, n = 5) and 5.1 +/- 0.3 microA/cm2 (n = 5) in 3-day and 17-day cells, respectively. When the charge carrier was Ba2+, the L-type Ca2+ channel current density was also smaller in 17-day cells (22.7 +/- 1.8 microA/cm2) than in 3-day cells (28.3 +/- 2.1 microA/cm2). In single-channel recordings, the mode-2 behavior was infrequent in 17-day cells compared with 3-day cells. High-open probability sweeps (with an open probability of greater than 0.25), reflecting mode-2 behavior, accounted for 20.2% and 3.7% in 3-day and 17-day cells, respectively. The ensemble-averaged currents in 17-day cells was 37% of that current in 3-day cells. In addition, decay of the averaged current appeared to be faster in 17-day cells than in 3-day cells. All data from the single-channel analysis agreed with the data from the whole-cell voltage clamp.(ABSTRACT TRUNCATED AT 250 WORDS)