12 W. A. DE VOOGD VAN DER StRAATEN 



Moreover the yield was not far below that obtained after homogenization followed 

 by extraction, and to take Hekkelman's own words, "the phenomenon suggests a 

 pumping out of cellular material". 



In a recent interesting publication (Peck et ai, 1964) we find another aspect of 

 the same problem. The authors describe the isolation of bone cells from rat calvaria 

 in buffered collagenase. The cells obtained passed successfully viability tests and 

 proved fit for cultivation. From cytochemical alkaline phosphatase reactions they 

 argue that their harvest probably contained osteoblasts and osteocytes. Moreover 

 radioassay of CO2 and lactate after confrontation with labelled glucose under aerobic 

 conditions revealed metabolic traits reminiscent of "intact" bone tissue. However they 

 observed no bone formation in tissue culture and were not able to prevent dedifferen- 

 tation and/or overgrowth by "fibroblasts". The latter point is not surprising at all. 

 Is the absence of bone formation surprising? Taking the acceptable view that bone 

 formation is a complex process dependent on the interplay of very subtle intra and 

 extra cellular conditions, the experiments clearly show that somewhere these condi- 

 tions were not fulfilled. However taking the biochemical data really to mean that the 

 collagenase isolated cells have preserved their original metabolic organization, we 

 come to the conclusion that perhaps even full knowledge concerning the metabolism 

 of the individual cells will always be fundamentally insufficient to explain the 

 formation of bone as a tissue. 



There is still another example to be considered In the clarification of my third 

 preliminary point. Starting with the assumption that destruction is in general easier 

 to understand than construction, one may be tempted to look upon the process of 

 osteoclastic bone resorption as a nut easy to crack. In fact it is not uncommon for the 

 specialist in tissue culture to be consulted about a method for cultivating osteoclasts 

 in pure strain for investigational purposes. The bare facts are that such a culture is 

 non existent and probably even impossible. Gaillard (1961) has repeatedly observed 

 in PTE treated cultivated radius rudiments that the numerous typical osteoclasts 

 disappear from the moment the bony shaft is totally resorbed. A good explanation 

 seems to be that the development or the preservation of typical osteoclasts depends 

 among other things on the presence of bone and/or breakdown products of bone. In 

 the light of work of Belanger we arrive at the same conclusion; however he adheres 

 to the restricting view that the development of the osteoclasts demands the presence 

 of bone. Returning to the observation of Gaillard and leaving undiscussed what, in 

 this situation, the fate of the osteoclasts might be, we conclude that the student of 

 osteoclastic function, working with isolated cells, would in all probability waste his 

 effort on cells in transition. 



Now coming to my main point and starting from the metabolic schemes known 

 from general biochemistry, what lines can be drawn in black and what lines have to 

 be dotted or even omitted? This specially concerns carbohydrate metabolism, which is 

 responsible for at least 3 diff'erent tasks in bone tissue: 1. Generation of energy; 

 2. Provision of the cells with precursors to be used in the synthesis of proteins, muco- 

 polysaccharides and pentose containing compounds of biological importance such as 

 the pyridine nucleotides and RNA and DNA; and 3. Production of organic acids 

 supposed to be important in the solubilization of matrix mineral. 



It is from histochemical investigations that we have at least some data concerning 

 the different types of cells (Balogh et al., 1961; Herrmann-Erlee, 1962). Balogh 



