LIPIDS PRESENT IN MUSCLES 731 



that, in the case of dogs, fat deposition occurred in the proximal tubules of 

 the kidney as well as in other organs, following chronic intoxication with 

 7-hexachlorocyclohexane. The kidney effect of the 5-isomer was less 

 marked, while D.D.T. did not cause any fat deposition in these organs. 



4. Lipids Present in the Muscles 



(1) Lipids in Different Types of Muscles 



The composition of the muscle lipids varies with the type of muscle in- 

 volved. There are three types, voluntary, cardiac, and involuntary. 

 The characteristic physiologic properties differ for each type. Bloor 190 

 describes these properties as follows : 



Voluntary or skeletal muscles are able to contract quickly and strongly, and can be 

 tetanized, but are not spontaneously active; they are capable of large expenditures of 

 energy; they have a single nerve supply, which is from the outside. 



Cardiac or heart muscles possess a spontaneous rhythmic activity; they have an ab- 

 solute refractory period, so that tetany is impossible, an "all or none" contraction, an 

 intrinsic nerve supply, and a regulatory nerve supply from the outside. 



Involuntary or smooth muscles have spontaneous rhythmic activity, ordinarily with 

 small tensions and slow motions requiring relatively small energy expenditure; there is 

 an intrinsic nerve net which insures spontaneous activity, and a regulatory nerve supply 

 from the outside. 



The lipids vary qualitatively and quantitatively with the type of muscle, 

 with the species of animal, with age, and with the amount of activity. 

 Of these three types of muscle, the cardiac muscle invariably has the highest 

 phospholipid content, while involuntary muscle has the highest and volun- 

 tary muscle the lowest cholesterol content. Although the heart may, in 

 some cases, have as high a cholesterol value as involuntary muscle, the 

 phospholipid : cholesterol ratio between these two muscles is quite different. 

 The P:C ratio for cardiac and voluntary muscle approximates 15:1, while 

 involuntary muscle has a 4:1 ratio. The neutral fat in the muscles is 

 similar to that in other fat depots. 191 Quagliariello 192 believes that the 

 lipids in the muscles are localized in the fibrils, and that they are absent 

 from sarcoplasm. 



Perry 193 was able to sediment lipoprotein granules by high-speed centri- 

 fugation of muscle homogenates from which the myofibrils and nuclei had 

 been removed. These lipoprotein granules possessed ATPase (adenosine 



190 W. R. Bloor, J. Biol. Chem., 114, 639-648 (1936). 



191 E. Klenk and F. Ditt, Z. physiol. Chem., 226, 213-220 (1934). 



192 G. Quagliariello, Arch, internat. physiol., 16, 239-250 (1921). 



193 S. V. Perry, Biochim. et Biophys. Acta, 8, 499-509 (1952). 



