IN VITRO STUDIES OF BONE RESORPTIVE MECHANISMS 



569 



normal lactate production by bone cells incubated at pH's as low 

 as 6.6. The simplest approach, therefore, was to incubate samples, 

 both fresh and inactivated, at lower pH's and see whether the differ- 

 ence between the two was abolished. Figure 8 shows the results ob- 



25 



20 



I 5 - 



10 - 



7.6 



7 4 



7.2 



7.0 



6 8 



6.6 



6.4 



6.2 



PH 



MEDIUM 



INC U BAT ION 



Fig. 8. The percentage increments in total calcium concentration main- 

 tained by fresh bone over heat-inactivated bone during aerobic incubation for 

 6 hours at 37.5°C in acetate buffers varying in pH from 7.1 to 6.2 have been 

 plotted with data from incubations in bicarbonate-buffered media at pH 7.6 

 and 7.4. Each point represents the mean of 4 to 6 observations. (This diagram 

 has been reproduced from Schartum and Nichols, 1962, where the details of 

 these experiments are discussed. It is reproduced with the permission of the 

 Journal of Clinical Investigation.) 



tained. It is apparent that the difference in Ca concentration be- 

 tween fresh and inactivated samples declined very sharply below 

 pH 7.2 and disappeared by pH 6.6, even though lactate production 

 was unchanged — a result which fits nicely with published data on 

 bone mineral solubility (Nordin, 1957). Thus on its first test the 



