Differential Ca2+ signaling in neonatal and adult rat hepatocyte doublets.
OBJECTIVE
Intracellular Ca2+ ([Ca2+]i) is important in various cellular functions, including cellular proliferation and differentiation. To elucidate the relationship between [Ca2+]i oscillations and physiological hepatocyte proliferation, phenylephrine-evoked [Ca2+]i responses were sequentially investigated using short-term cultured hepatocyte doublets obtained from 1-, 3-, 6- and 8-week-old rats.


RESULTS
DNA synthesis in hepatocytes, determined by BrdU incorporation, was approximately 20% in 1-week-old rats, and decreased to <1% as the rats aged. Correspondingly, [Ca2+]i responses evoked by 10 micromol/l phenylephrine in hepatocyte doublets shifted from transient to sinusoidal-type [Ca2+]i oscillations and then to a sustained increase in [Ca2+]i, followed by a gradual return to baseline. The incidence of [Ca2+]i oscillations was 100+/-0.0%, 83.3+/-16.7%, 38.7+/-0.6% and 5.5+/-5.0% in 1-, 3-, 6- and 8-week-old rats, respectively. Removal of extracellular Ca2+ did not abolish [Ca2+]i oscillations, indicating that [Ca2+]i oscillations were caused primarily by Ca2+ mobilization from internal sites of the cells. The [Ca2+]i level in each of the adjacent cells was synchronous in sustained increase in [Ca2+]i, but asynchronous in [Ca2+]i oscillations. In proliferating doublets obtained from 1-week-old rats, the frequency of oscillations increased in a dose-dependent manner for phenylephrine concentrations of 1 to 100 micromol/l.


CONCLUSIONS
Phenylephrine-evoked [Ca2+]i oscillations were directly related to hepatocyte proliferation and were mediated by frequency modulation. These results suggest that phenylephrine-evoked [Ca2+]i oscillations may contribute to cell-cycle progression of hepatocytes in physiological liver growth.
Enomoto
N
N
Department of Gastroenterology, Juntendo University School of Medicine, Tokyo, Japan.
Kitamura
T
T
Hirose
M
M
Ikejima
K
K
Watanabe
S
S
Sato
N
N
D000818:Animals; D000831:Animals, Newborn; D001973:Bromodeoxyuridine; D002118:Calcium / Q000502:physiology*; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D005260:Female; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009991:Oscillometry; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013194:Staining and Labeling
D010656:Phenylephrine; D001973:Bromodeoxyuridine; D002118:Calcium