[1] Univ Texas Med Branch, Sealy Ctr Aging, Galveston, TX 77555 USA
[2] Univ Kentucky, Dept Physiol, Coll Med, Lexington, KY 40506 USA
[3] Univ Kentucky, Sanders Brown Ctr Aging, Lexington, KY 40536 USA
[4] Univ Kentucky, Dept Biostat, Coll Publ Hlth, Lexington, KY 40536 USA