Some Remarks and Questions on Metabolic Patterns in the Family of Bone Cells 1 1 



tional definition linking up the specific biochemical organization and the specific 

 function of the cell. However we will soon find out that our definition is a little 

 pedantic as our present day knowledge hardly allows for even one single good 

 example. 



3. The final preliminary point will carry us forward to the heart of our subject. 

 The number of publications concerning the metabolism of bone cells is increasing, and 

 it is already apparent that there is a wide difference in scope and method among the 

 various approaches. Concerning differences in scope there are two extremes. At one 

 end we find investigations disclosing the activity of the cellular enzymatic apparatus. 

 At the other end investigations dealing with the fate of certain substrates. Figuratively 

 speaking one could say that the first group deals with the metabolic highway system 

 of the cells, the other group with the real traffic on that highway system. This picture 

 will make clear to us that the conditions of the highways and the intensity of the 

 traffic do not necessarily run parallel. 



Concerning differences in method, we can more or less arbitrarily differentiate 

 into methods that carry no considerable risk of changing the metabolic parameters 

 under investigation and methods that do. To my mind histochemical and enzymo- 

 logical investigations performed on previously intact bone tissue fall within the group 

 of low risk. However metabolic investigations using slices or otherwise wounded 

 pieces of bone tissue ask for a more critical attitude. And in fact without any data at 

 hand one can foresee that e. g. by damaging the delicate network of osteocytes serious 

 harm is probably done. 



In this connection unpublished data from Hekkelman (personal communication) 

 have illustrative value: He observed that pieces of diaphyseal rabbit bone (roughly 

 15X5X2= 150 mm-*) put in Hanks balanced salt solution lose a considerable amount 



Table 1. The total amount of nucleic acid obtained after 2 hours of incubation and expressed 

 as ugjml incubation fluid from 'Is g of hone 



Hanks (ph 7.4) , 2.7 ± 0.77 , 6.6 ± 1.96 | < 0.002 



(6 exp.) I (6 exp.) 

 Hanks without glucose (ph 7.4) 3.2 ± 0.4 4.3 ±1.2 ! < 0.01 



! (6 exp.) (12 exp.) 



Pd insignificant < 0.01 



Table 2. The activity of isocitric dehydrogenase obtained in the medium after 2 hours of 

 incubation: mu moles/minig of bone 



Hanks (ph 7.4) 6.28 + 2.2 13.2 ± 5.6 0.02 > p > 0.01 



(6 exp.) (6 exp.) 



Hanks without glucose (ph 7.4) 4.82 ±1.3 6.42 4- 4.41 insignificant 



(9 exp.) (l?cxp.) 



Pd I insignificant 0,02 > p > 0.01 



of nucleic acid and enzymes as e. g. isocitric and lactic dehydrogenase. The output 

 was found to depend on the temperature of incubation and the presence or absence 

 of glucose; see Tables 1 and 2. 



