Abstract 312: Mechanisms Underlying Impaired KCl-induced Contractility After Long-term Serum-free Organ-culture of Rat Isolated Mesenteric Artery
(Background and aim) Organ culture of blood vessels is a useful technique to investigate the long-term effects of drugs. Organ culture in a serum-free condition is so far the best way to maintain differentiated cell function. However some functional changes may occur from freshly isolated blood vessel (fresh) such as decreased contractility. Mammalian/mechanical target of rapamycin (mTOR) complex 1 is atypical serine/threonine kinase which integrates various signals induced by growth factors, stress, energy status, oxygen, and amino acids. Here, we investigated the mechanism of decrease in smooth muscle contractility after long-term serum-free organ culture specifically focusing on mTOR.
(Methods and results) Rat isolated mesenteric arteries were cultured for 5 days without (0% serum) or with rapamycin (Rap). In 0% serum, absolute contraction by KCl significantly decreased from fresh (n=21 for fresh, n=7 for 0% serum, p<0.01). In Rap, the decreased contraction was significantly normalized (n=7, p<0.05 vs. 0% serum). In both 0% serum and Rap, sensitivity to KCl significantly increased from fresh (p<0.01 vs. fresh). In 0% serum, mTOR expression significantly increased from fresh (n=8, p<0.01) which was significantly normalized by rapamycin (n=8, p<0.01). Morphological examinations showed degenerative changes in smooth muscle layer of 0% serum which was improved by rapamycin. In 0% serum, expression of myocardin, a master regulator of smooth muscle gene expression significantly decreased from fresh (n=9, p<0.01), which was significantly normalized by rapamycin (n=9, p<0.01).
(Conclusion) Addition of rapamycin prevented the decreased contractility in serum-free organ cultured mesenteric artery perhaps by normalizing the mTOR and downstream myocardin expression as well as arterial degenerative morphological damage. Further studies are needed to clarify how mTOR controls myocardin expression and also how decreased myocardin expression leads to the decreased smooth muscle contractility. This experimental system may be useful for the hypertension research.
- © 2013 by American Heart Association, Inc.