Systems specificity in responsiveness to intermittent artificial gravity during simulated microgravity in rats.

It has been shown that the minimum gravity exposure requirements vary greatly among different physiological systems. A preliminary comparison between two extremes, vessels vs. bones, shows that not only the mechanostat at the tissue level differs greatly, but also the bone loss during weightlessness may also involve calcium deposition-resorption changes. It seems that the surprising efficacy of intermittent artificial gravity (IAG) is due to the vascular tissues possessing a strong resilience or "memory" function toward restoring their original pre-stress and tensegrity state at the 1 G environment. It appears that the bone tissue is related to a more complex tensegrity paradigm involving both osteoblasts and osteoclasts, and a longer half time for calcium deposition-absorption. Cell-level models (CellML) for calcium dynamics is currently available. We hope that the Physiome Project can use this modeling framework to help interpret the resistance of bones to IAG and to evaluate whether the "intermittent" or "continuous" AG scheme should be adopted eventually for future exploration-class spaceflight.