Use of A-192621 to provide evidence for involvement of endothelin ETB-receptors in endothelin-1-mediated cardiomyocyte hypertrophy

Increased plasma levels of endothelin-1 correlate with the severity of left ventricular hypertrophy in vivo. The aim of the study was to determine the relative contribution of stimulation of endothelin ETA and endothelin ETB receptors, and the associated activation of protein kinase C, to the hypertrophic response initiated by endothelin-1 in adult rat ventricular cardiomyocytes maintained in culture (24 h). Endothelin-1 (10(-7) M) increased the total mass of protein and the incorporation of [C-14] phenylalanine into protein to 26% and 25% greater (P < 0.05) than respective basal values. The total content of RNA and the incorporation of 2-[C-14] uridine into RNA were increased by 23% and 21%, respectively, by endothelin-1 (10(-8) M). Actinomycin D (5 X 10(-6) M), an inhibitor of transcription, abolished the incorporation of [C-14] phenylalanine and the increased protein mass elicited by endothelin-1 (10(-8) M). The selective agonists at the endothelin ETB receptor, sarafotoxin 6c (10(-7) M) and endothelin-3 (10(-7) M), increased the incorporation of [C-14] phenylalanine to 13% and 13% greater than respective basal values. The incorporation of [C-14]phenylalanine in response to endothelin-1 (10(-7) M) was reduced by 50% (P < 0.05) by the selective antagonist at endothelin ETA receptors, ABT-627 (10(-9) M), while the response to sarafotoxin 6c was not attenuated. The selective antagonist at endothelin ETB receptors, A192621 (10(-10) M), abolished the response to sarafotoxin 6c (10(-7) M) and attenuated the response to endothelin-l (10(-7) M) by 43% (P < 0.05). The selective inhibitor of protein kinase C, bisindolylmaleimide (5 X 10(-6) M) attenuated the response to sarafotoxin 6c (10(-7) M) by 78% and that to endothelin-1 (10(-7) M), elicited in the presence of A192621 (10(-10) M), by 52%. In conclusion, these data implicate endothelin ETB receptors, in addition to endothelin ETA receptors, in endothelin-1-mediated cardiomyocyte hypertrophy and provide evidence for the involvement of protein kinase C, at least in part, in the hypertrophic signalling pathways associated with activation of each receptor subpopulation. (C) 2001 Elsevier Science B.V. All rights reserved.