Mechanisms underlying a decrease in KCl-induced contraction after long-term serum-free organ culture of rat isolated...

Area of Science:

• Vascular biology
• Pharmacology
• Cellular signaling

Background:

• Organ culture of blood vessels is crucial for studying long-term drug effects.
• Freshly isolated vessels may undergo functional changes during culture.
• Mechanistic target of rapamycin (mTOR) influences smooth muscle differentiation and calcium (Ca2+) mobilization.

Purpose of the Study:

• To investigate the mechanisms behind altered smooth muscle contractility in serum-free organ culture.
• To determine the role of mTOR in these functional changes.
• To assess the impact of rapamycin on smooth muscle function during culture.

Main Methods:

• Rat isolated mesenteric arteries were cultured for 5 days.
• Cultures were maintained in either 0% serum or 0% serum with rapamycin.
• Vessel contractility, mTOR expression, myocardin, and contractile protein levels were analyzed.

Main Results:

• Serum-free culture decreased KCl-induced contraction, which rapamycin rescued.
• mTOR expression increased in serum-free culture, and rapamycin normalized it.
• Myocardin expression decreased, but contractile proteins (SM22α, calponin) were unaffected by rapamycin.
• Calmodulin-dependent protein kinase II phosphorylation increased and caffeine-induced contraction decreased, both rescued by rapamycin.

Conclusions:

• Serum-free organ culture increases mTOR expression in rat mesenteric arteries.
• Elevated mTOR may contribute to decreased smooth muscle contractility, potentially via reduced Ca2+ storage.
• Rapamycin can mitigate culture-induced alterations in vascular smooth muscle function.