IN VIVO I-UNCTION OF Sl'BCULLUL \R PARTICLliS 



17 



on work liy I'arhcr and associates ( 10) with succinic dehydrogenase, antl on un- 

 published work in our own kiboratory with DPNH oxidation. When tetrazoHuni 

 accepts electrons it precipitates as a brightly-colored insoluble tormazan. 



Figures 18 and 19 are from frozen sections of forniol-calcium fixed tissue, 

 incubatetl with DPNH as substrate and the new 'Nitro-BT' of Tsou, Nachlas 

 and Seligman (56) as the tetrazolium salt. The activity visualized is that portion 

 of DPNH-cytochrome c reductase which survives cold formol-calcium fixation. 

 The best name for this portion of the electron transport chain would be the opera- 

 tional term, DPNH-tetrazolium reductase. Tn heart, vividly-stained mitochondria 

 are readily seen (fig. 18). On the other hand, ni liver (tig. 19) mitochondria are 

 difficult to discern, except in areas. We believe this results partly because of damage 

 to the mitochondria, but largely because of the abundant ergastoplasm with high 

 I^PNH-cytochrome c reductase activity. This produces formazan throughout the 

 cell, obscuring the mitochondria. When liver mitochondria are isolated and then 

 incubatetl in the same medium, their staining is readily seen. Thus, the staining 

 results agree well with the data on isolated fractions which show DPNH-cyto- 

 chrome c reductase activity in both microsomes and mitochondria. 



Fig. 18. DPNH-tetrazoliuin reductase activity in frozen section of rat heart Hxeil in torinol- 

 calcium. Note darkly-stained mitochondria. X 9<'"- 



Fig. 19. DPNH-tetrazolium reiluctase acti\it\ in frozen section of rat liver hxed in lormol- 

 calcium. The granular precijiitate over parenchymatous cells makes mitochondria diflicuit to 

 see, except in areas. Within the portal space, the arteriole sections show deeply-stained smooth 

 muscle cells. X 580. 



