Appearance of contractile endothelin‐B receptors in rat mesenteric arterial segments following organ culture

The aim of this study was to examine how different procedures for organ culture affect the expression of contractile endothelin(ET)‐B receptors in a branch of the rat mesenteric artery. In fresh segments, ET‐1 and ET‐3 induced similar strong contractions, ET‐1 being 20‐fold more potent, whereas neither of the selective ET B receptor agonists, sarafotoxin 6c (S6c) nor IRL 1620, induced significant contractions. In segments cultured for 1 day, ET‐3 was only 3‐fold less potent as ET‐1, and S6c and IRL 1620 induced concentration‐dependent contractions which were about 60% of the ET‐1 induced contraction. The maximum contractile response to S6c was not altered in segments cultured with foetal calf serum or in buffer solution, but was reduced to about 20% of the control value when cultured in glucose‐free buffer solution. The contraction to S6c was abolished in segments placed in cold (4 °C) buffer solution. Removal of the endothelium had no effect on the S6c‐induced contractions. Arteries cultured at isometric tension (at 2 mN) for 1day achieved the same contractile response for ET B agonists as resting segments. Pressurized arteries (60 mmHg) did not constrict to S6c when mounted as a fresh segment but demonstrated a strong contraction after 1 day at this transmural pressure. This study suggests that the appearance of ET B receptor mediated contraction following organ culture is not dependent on specific nutrients, endothelial factors or absence of intrinsic tension, but is a metabolically active process.