|Budget Amount *help
¥3,500,000 (Direct Cost : ¥3,500,000)
Fiscal Year 1998 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 1997 : ¥2,000,000 (Direct Cost : ¥2,000,000)
Angiotensin II has been shown tobe mitogenic in various cell types. In cultured neonatal cardiomyocytes, we have demonstrated that angiotensin II causes hypertrophy, not hyperplasia. However, fetal or neonatal cardiomyocytes exhibit limited proliferation in primary culture, and are mitotically less potent. In order to determine whether angiotensin II is simply a hypertrophic or hyperplastic growth factor for mitotically potent cardiomyocytes, we analyzed [^3H]-Thymidine uptake and cell cycle-regulated gene expression using SV4O large T-transformed AT-1 cardiomyocytes. Angiotensin II, alone and in combination with other growth factors, increased [^3H]-Thymidine uptake in a dose-dependent manner. The mRNA expression of G1 cyclin (Cyclin C, Dl, D2, D3) and histone H1-kinase activity by cdk2 increased 6 h after angiotensin II stimulation Westernblot analysis revealed cyclin B1 expression after 18 h, which peaked at 30 h. Histone Hi-kinase activity by cdc2 was also increased by angiotensin II, and peaked at 24 - 36 h, indicating that these changes were cell cycle dependent. Double immunofluorescent photography showed that AT-1 cells incorporated BrdU, and expressed cdc2 by angiotensin II stimulation [^3H]-Thymidine and BrdU uptake were blocked by Losartan, but not by PD123319. Incontrast with neonatal cardiomyocyte, angiotensin II potentiated DNA synthesis and induced cell cycle regulated gene expression in AT-1 cardiomyocytes, and this activity was mediated by the angiotensin II type-1 receptor.