Rapid functional upregulation of vasocontractile endothelin ETB receptors in rat coronary arteries

Abstract

AimsEndothelin ETB receptors mediate under normal physiological conditions vasorelaxation in coronary arteries. However, vasocontractile ETB receptors appear in coronary arteries of ischemic heart disease patients. Interestingly, organ culture of isolated coronary arteries also induces upregulation of vasocontractile ETB receptors. This study examines the early time course and mechanism behind upregulation of contractile ETB receptors in isolated rat coronary arteries during short-term organ culture. Main methodsCoronary artery segments were mounted in wire-myographs and incubated in physiological saline solution. Contractions were measured after exposure to the specific ETB receptor agonist Sarafotoxin 6c (S6c) and the endogenous agonists endothelin-1 and endothelin-3. Protein localization and levels of ETB and phosphorylated-extracellular-signal-regulated-kinase-1/2 (ERK1/2) were examined by immunohistochemistry. Key findingsFresh arteries showed negligible vasoconstriction to S6c. However, incubation for only 4 and 7h increased S6c contractions two- and seven-fold, respectively. Furthermore, 7h incubation enhanced vasocontractile responses to endothelin-3 and increased ETB receptor density in vascular smooth muscle cells. ERK1/2 was activated rapidly after start of incubation. Moreover, incubation with either the transcriptional inhibitor actinomycin D or the mitogen-activated-protein kinase kinase 1/2 (MEK1/2) inhibitor U0126 attenuated contractile ETB receptor upregulation. U0126 attenuated ETB receptor protein levels after 24h of incubation. SignificanceCoronary arteries rapidly upregulate vasocontractile ETB receptors during organ culture via transcriptional mechanisms and MEK-ERK1/2 signalling. This model may mimic the mechanisms seen in ischemic conditions. Furthermore, these findings have important experimental implications in tissue bath experiments lasting for more than 4h.