COMPARATIVE EFFECTS OF CONTRACTION AND ANGIOTENSIN-II ON GROWTH OF ADULT FELINE CARDIOCYTES IN PRIMARY CULTURE

The purposes of this study were 1) to determine whether angiotensin II causes growth of adult feline cardiocytes in long-term culture, 2) to compare the growth effects of angiotensin II with those resulting fro m electrically stimulated contraction, and 3) to determine whether the anabolic effects of contraction are exerted via the angiotensin type 1 receptor. Adult feline cardiocytes were cultured on laminin-coated t rays in a serum-free medium. Cardiocytes were either electrically stim ulated to contract (1 Hz, 5-ms pulse duration, alternating polarity) o r were nonstimulated and quiescent. Quiescent cells were studied as co ntrols and after treatment with angiotensin II (10(-8) M), losartan (1 0(-6) M; an angiotensin type 1-receptor antagonist), or angiotensin II plus losartan. Contracting cells were studied in the presence and abs ence of angiotensin II or losartan. In quiescent cardiocytes, angioten sin II treatment on day 7 significantly increased protein synthesis ra tes by 22% and protein content per cell by 17%. The effects of angiote nsin II were completely blocked by losartan. Electrically stimulated c ontraction on days 4 and 7 in culture significantly increased protein synthesis rate by 18 and 38% and protein content per cell by 19 and 46 %, respectively. Angiotensin II treatment did not further increase pro tein synthesis rate or protein content in contracting cardiocytes. Fur thermore, losartan did not block the anabolic effects of contraction o n protein synthesis rates or protein content. In conclusion, angiotens in II can exert a modest anabolic effect on adult feline cardiocytes i n culture. In contracting feline cardiocytes, angiotensin II has no ef fect on growth. Growth caused by electrically stimulated contraction o ccurs more rapidly and is greater in magnitude than that caused by ang iotensin II. Growth of contracting adult feline cardiocytes is not dep endent on activation of the angiotensin receptor.