566 



G. NICHOLS, JR. 



I 50- 



130- 



H < 



SO- 



TO 



NORMAL BONE 



ia BONE 



Fig. 6. Components of the total calcium concentration maintained in incu- 

 bation media at "steady state" by metaphyseal bone from normal and ia rats 

 22 days old. Conditions of incubation, etc., were as in previous figures. The 

 large increment in the fraction of the total calciimi concentration dependent 

 on cellular activity in ia bone can be seen to account entirely for the 60 per 

 cent increment above controls in the total Ca concentration found in media 

 surrounding fresh samples. (These data have been replotted from \"aes and 

 Nichols, 1963.) 



same, but the level maintained by living bone is much higher in 

 ia animals. Thus, in this case, the increment in fresh bone is entirely 

 in the fraction dependent on cellular acti\ itv. The reason for this 

 difference between normal and ia rats remains unknown, but met- 

 abolic studies have shown no excessive lactate or citrate accumula- 

 tion in the medium surrounding ia bone, although a partial defect 

 in citrate oxidation appears to be present. 



Although these experiments illustrated se\'eral important features 

 of the distribution of Ca and P between bone and its surrounding 

 fluids, the information needed to relate cellular metabolic activity 

 directly to Ca and P mobilization into the medium and to changes 

 in bone mineral solubility was still lacking. In all these experiments, 

 however, the in vitro svstem had been viewed, na'ivelv, as a two- 

 phase system, bone and medium. It became increasingly apparent 



