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

Aims: Endothelin ET(B) receptors mediate under normal physiological conditions vasorelaxation in coronary arteries. However, vasocontractile ET(B) receptors appear in coronary arteries of ischemic heart disease patients. Interestingly, organ culture of isolated coronary arteries also induces upregulation of vasocontractile ET(B) receptors. This study examines the early time course and mechanism behind upregulation of contractile ET(B) receptors in isolated rat coronary arteries during short-term organ culture.

Main Methods: Coronary artery segments were mounted in wire-myographs and incubated in physiological saline solution. Contractions were measured after exposure to the specific ET(B) receptor agonist Sarafotoxin 6c (S6c) and the endogenous agonists endothelin-1 and endothelin-3. Protein localization and levels of ET(B) and phosphorylated-extracellular-signal-regulated-kinase-1/2 (ERK1/2) were examined by immunohistochemistry.

Key Findings: Fresh 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 ET(B) 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 ET(B) receptor upregulation. U0126 attenuated ET(B) receptor protein levels after 24 h of incubation.

Significance: Coronary arteries rapidly upregulate vasocontractile ET(B) 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.