2-chloroadenosine increases calcium mobilization from mouse calvaria in vitro

The effect of 2-chloroadenosine on bone resorption and on cyclic AMP formation in murine calvarial bones in vitro was investigated. 2-Chloroadenosine increased the release of 45Ca from the cultured bones, but had no effect on dead bones, indicating that the effect is cell mediated. The adenosine analogue remained in the medium for 48 h and caused a transient stimulation of the formation of cyclic AMP. The dose-response curve for the stimulatory effect on cyclic AMP accumulation was linear up to 10(-4) M. The dose-response curve for 45Ca release was liner from 3 x 10(-7) M to 3 x 10(-5) M but then showed a decline in the response. 8-Bromo cyclic AMP inhibited the release of 45Ca in 24 h cultures. The initial stimulatory effect on bone resorption by 2-chloroadenosine may therefore not depend on cyclic AMP. The level of inosine increased during culture indicating that adenosine is formed by bone tissue.