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

Abstract

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 ET A and endothelin ET B 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 [ 14C] 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-[ 14C] uridine into RNA were increased by 23% and 21%, respectively, by endothelin-1 (10 −8 M). Actinomycin D (5×10 −6 M), an inhibitor of transcription, abolished the incorporation of [ 14C] phenylalanine and the increased protein mass elicited by endothelin-1 (10 −8 M). The selective agonists at the endothelin ET B receptor, sarafotoxin 6c (10 −7 M) and endothelin-3 (10 −7 M) , increased the incorporation of [ 14C] phenylalanine to 13% and 13% greater than respective basal values. The incorporation of [ 14C]phenylalanine in response to endothelin-1 (10 −7 M) was reduced by 50% ( P<0.05) by the selective antagonist at endothelin ET A receptors, ABT-627 (10 −9 M), while the response to sarafotoxin 6c was not attenuated. The selective antagonist at endothelin ET B receptors, A192621 (10 −10 M), abolished the response to sarafotoxin 6c (10 −7 M) and attenuated the response to endothelin-1 (10 −7 M) by 43% ( P<0.05). The selective inhibitor of protein kinase C, bisindolylmaleimide (5×10 −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 ET B receptors, in addition to endothelin ET A 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.