Pooneh Bagher

Abstract Space exploration is important for scientific discovery, advancing technology, and the long-term survival of humanity. However, the impacts of microgravity and cosmic radiation during space travel on human physiology are not completely understood. While microgravity results in a loss of skeletal muscle mass and function, the effect on cardiac muscle, in particular the contractile elements, is not as clear.

Introduction In vascular smooth muscle (VSM), contraction is initiated by phosphorylation of the regulatory light chain (RLC20) of SM myosin II on Ser19 by the SM myosin light chain kinase (smMLCK, referred to hereafter as MLCK). MLCK is activated by Ca2+-bound calmodulin (CaM). (Gallagher et al., 1992; Hartshorne et al., 1998).

Vasoconstriction must be balanced with vasodilation, particularly in the arterioles that supply tissues with blood. Endothelial cells protrude through holes in the internal elastic lamina in arterioles to make contact with vascular smooth muscle cells. Gap junctions are present at these sites where endothelial cells meet vascular smooth muscle cells. IP 3 has been thought to be a signal that passes through these gap junctions to endothelial cells to mediate vasodilation. However, Garland et al.