IN VITRO STUDIES OF BONE RESORPTIVE MECHANISMS 



561 



0.80- 



0.60 



0.40 



0.20 



0.00 



• SURVl VING BONES 



O HEAT- I NACTI VATED BONES 



3 6 9 12 

 HOURS OF INCUBATION 



Fig. 2. Calcium concentrations found in incubation media surrounding 

 fresh and heat-inactivated calvaria from 7- to 9-week-old mice after various 

 periods of incubation. Krebs-Ringer media (pH 7.4) buffered with bicarbonate, 

 a gas phase of 5 per cent COo and air, and glucose 2 mg/ml as substrate were 

 used. No calcium was present in the media at the start of incubation, but 

 phosphorus 0.4 mmole/ liter was included. Calvaria were inactivated by im- 

 mersion for 1.5 minutes in medium previously brought to boiling. A "steady 

 state" distribution of Ca and P between bone sample and incubation medium 

 was assumed to hold after 4 hours of incubation on the basis of these findings. 

 (This diagram has been reproduced from Schartum and Nichols, 1961^, with 

 the permission of the Journal of Clinical Investigation. ) 



periments using calvaria from mice, Schartum was able to show, as 

 indicated in Fig. 2, that the Ca concentration in incubation medium 

 (Ca-free at the start of the experiment) rapidly reached a plateau, 

 and the level maintained by fresh bone, which was producing acid, 

 was 18 per cent higher than that maintained by inactivated bone 

 which produced no acid. On the basis of this observation the total 



