5()2 G. NICHOLS, JR. 



medium Ca concentration at steach state in vitro could he divided 

 into two fractions: one dependent on mineral solubility alone — the 

 concentration maintained by inactive bone — and an additional in- 

 crement dependent on the presence of cell metabolism. Moreover, 



100 



CALCIUM 



LACTATE 



COHTROUS HEATED , , „" °„ 3 , '" "", ^'uf^ " ' "">"0B. 



Fig. 3. Ca++ and lactate" concentrations in incubation media after 6 

 hours' incubation of calvaria from 7- to 9-week-old mice. Krebs-Ringer bicar- 

 bonate-buffered media, containing no Ca++ but 0.4 mmole/liter of phosphorus, 

 and a temperature of 37.5°C were used. The gas phase was 5 per cent COo 

 in air or No as appropriate. Glucose when present was at a concentration of 

 2 mg/ml. lodoacetate when used was added to give a final concentration of 

 0.9 X 10-^ M. The data in this diagram have been plotted as percentages of 

 the values obtained in simultaneous aerobic incubations of normal samples in 

 media containing glucose and no inhibitors. The scale for calcium is on the left, 

 for lactate on the right. (The data shown have been recalculated from Schar- 

 tum and Nichols, 19615.) 



metabolic acid production and this increment in Ca concentration 

 in the media seemed at least qualitatively related. 



His next series of experiments is summarized in Fig. 3. Previous 

 experience (Borle, Nichols, and Karnovsky, 1960; Kenny, 1961) in- 

 dicated that lactate and H+ ion accumulation in the medium could 

 be increased by incubation under N2 and sharply reduced by the 

 omission of glucose from the medium or by metabolic inhibitors. 



