| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1997: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1996: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Research Abstract |
We recently reported characteristic [Ca^<2+>]_i oscillations in hepatocytes derived from livers regenerating in response to 66% hepatectomy (Hepatology 21 ; 1395-1404,1995). To further characterize [Ca^<2+>]_i responses during hepatocyte proliferation and differentiation, we investigated phenylephrine-evoked Ca^<2+> responses in (1) primary cultured hepatocyte doublets from physiologically growing liver, and (2) rat hepatocytes that were conditionally immortalized by retroviral transduction with a thermolabile mutant SV40 large T antigen (SV40^<ts>T hepatocytes).
In hepatocytes obtained from 1-8 week-old rats, [Ca^<2+>]_i oscillations were most frequently observed in 1 week rats, and thereafter replaced by sustained increase in [Ca^<2+>]_i in 8 week rats, suggesting that [Ca^<2+>]_i oscillations might regulate cell-cycle progression in physiological liver growth.
When SV40^<ts>T hepatocytes were stimulated with phenylephrine, the non-proliferating cells (cultured at 39ﾟC) presented a non-oscillatory sustained increase in [Ca^<2+>]_i in the presence of extracellular Ca^<2+>, the duration of which was attenuated in the absence of extracellular Ca^<2+>.In contrast, proliferating hepatocytes (cultured at 33ﾟC) showed a transient, but not sustained increase in [Ca^<2+>]_i both in the presence or absence of extracellular Ca^<2+>.
In conclusion, SV40^<ts>T hepatocytes exhibit different Ca^<2+> responses during proliferation and differentiation.In contrast to the findings in hepatocytes from physiologically growing liver, the immortalized hepatocytes undergoing mitosis due to the presence of SV40 T antigen in their nuclei did not display [Ca^<2+>]_i oscillations, suggesting a difference in the mechanisms of proliferation initiation between these cells.
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