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J Appl Physiol 102: 1595-1603, 2007. First published January 11, 2007; doi:10.1152/japplphysiol.01020.2006
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Simulated microgravity effects on the rat carotid and femoral arteries: role of contractile protein expression and mechanical properties of the vessel wall

Department of Pharmacology, School of Medicine, University of California, Irvine, California

Submitted 12 September 2006 ; accepted in final form 2 January 2007

The goal of this study was to determine the effects of microgravity on myofilament protein expression and both passive and active length-force relationships in carotid and femoral arteries. Microgravity was simulated by 20-day hindlimb unweighting (HU) in Wistar male rats, and carotid and femoral artery segments were isolated from both HU and control (CTL) rats for Western blot and length-force analysis. Western blots revealed that HU significantly decreased myosin light chain-20 (MLC-20) protein levels in both carotid and femoral arteries and decreased myosin heavy chain (MHC) in femoral artery. -Actin levels were not altered by HU treatment in either artery. Length-force analysis demonstrated that HU did not change either passive or active length-force relationships in the femoral artery. HU-treated arterial rings developed significantly less force to 100 mM K⁺ than CTL, but optimal lengths were identical. In the carotid artery, length-active force curves were identical for both CTL and HU; however the length-passive force curve for HU-treated rings exhibited a steeper slope than CTL, suggesting decreased compliance of the artery wall. In conclusion, our data suggest that the HU-induced decreases in both MLC-20 and MHC in femoral artery are responsible for the decreased contraction to 100 mM K⁺ in HU-treated femoral artery rings. In the carotid artery, the HU-induced decrease in vessel wall compliance may counter any decrease in contractility caused by the decreased MLC-20 levels.

hindlimb unweighting; deoxyribonucleic acid; actin; myosin; length-force relationship

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