Effect of simulated microgravity on contractility, contractile protein expression and vascular compliance

Abstract

The goal of the present study was to determine the effects of simulated microgravity on contractile protein expression, assessed by Western analysis, and the passive and active length-force relationships, assessed by wire myography, in endothelium-denuded femoral and carotid arteries. Microgravity was simulated over 20 days using hindlimb unweighting (HU) in rats, and 3mm artery rings were isolated for in vitro analysis. HU markedly reduced the expression of myosin light chain 20 (MLC-20) in both carotid and femoral arteries, and of myosin heavy chain (MHC) in femoral artery. Alpha actin did not change. In femoral artery, HU had no effect on either passive or active (100 mM K+) length-force relationships. Optimal diameters were identical, but HU rings developed significantly less force, than control (C). HU carotid arteries exhibited a steeper passive length-force curve; i.e., HU increased carotid artery stiffness. In contrast, C and HU carotid artery active length-force curves were superimposable, yielding identical optimal diameters and maximal forces developed. It is suggested that the decreases in MLC-20 and MHC in femoral artery were responsible for the HU-induced reduction in the 100 mM K+-mediated contraction. The failure of HU to alter the contractile capacity of carotid artery may be due to the opposing effects of the increased vessel stiffness versus the reduced expression of MLC-20. NASA Grant NNA04CK29G.