INVOLVEMENT OF ENDOTHELIN (ET)A AND ETB RECEPTORS IN THE HYPERTROPHICEFFECTS OF ET-1 IN RABBIT VENTRICULAR CARDIOMYOCYTES

The question was addressed whether endothelin-1 (ET-1) exerts hypertro phic effects in cardiomyocytes isolated from ventricles of adult rabbi ts and maintained in short-term (24 h) serum-free primary culture prov iding mechanical quiescence. ET-1 (greater than or equal to 100 pM) in creased significantly total mass of cellular protein and incorporation of L-U-[C-14]phenylalanine and 2-[C-14]uridine into cellular protein and RNA, respectively. Cycloheximide (35 mu M), an inhibitor of protei n synthesis, significantly reduced the incorporation of L-U-[C-14]phen ylalanine and 2-[C-14]uridine into cellular protein and RNA, respectiv ely, under control conditions and in response to ET-1. Actinomycin D ( 5 mu M), a selective inhibitor of transcription, abolished the incorpo ration of 2-[C-14]uridine into cellular RNA and significantly reduced the incorporation of L-U-[C-14]phenylalanine into cellular protein und er control conditions and in response to ET-1. The selective antagonis ts at the ETA receptor [BQ123 (100 nM) and PD155080 (100 nM)] and the selective antagonist at the ETB receptor [BQ788 (100 nM)] significantl y reduced the incorporation of L-U-[C-14]phenylalanine into cellular p rotein in response to ET-1 (10 nM). The selective inhibitor of protein kinase C (PKC), bisindolylmaleimide (BIM) (5 mu M), reduced markedly the incorporation of 2-[C-14]uridine into cellular RNA and, to a lesse r degree, the incorporation of L-U-[C-14]phenylalanine into cellular p rotein in response to ET-1 (100 pM to 10 nM). ET-1 exerts hypertrophic effects directly in vitro in ventricular cardiomyocytes isolated from the hearts of adult rabbits. These effects are (a) due to de novo syn thesis since total mass of cellular protein and incorporation of L-U-[ C-14]phenylalanine and 2-[C-14]uridine into cellular protein and RNA, respectively, were increased; (b) mediated by both the ETA and ETB rec eptor subtypes; and (c) may be associated, at least partly, with the a ctivation of PKC.