Microgravity in space has been reported to enhance bone resorption in vitro and in vivo, however, the gravity effect on bone remodeling is not well understood. In particular, there are only a few reports about gravity effect on osteoclasts. In the present study, we examined the hypergravity effect on mRNA expressions of osteoclast marker enzymes such as TRAP (tartrate-resistant acid phosphatase) and cathepsin K. Osteoclasts were exposed to 30 x g for 2 hr or 18 hr. Results suggested that hypergravity enhanced the mRNA expression of both enzymes with different manner; the expression of the TRAP showed a slight increase, that of the cathepsin K showed a non-monotonous time course with maximum hypergravity effect for short time (2 hr) incubation.
