. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Nervous Systems 781 The plasma membrane is lipoprotein, as indicated by much indirect evi- dence. Certain electrochemical properties of the lipoprotein membrane seem to be imparted by a substance that is a quaternary ammonium base, the synthesis of which requires sodium.^"^ Specific aromatic hydrocarbons and other non-polar molecules depolarize, apparently by adsorbing on receptor areas of less than 8 'A;~ calcium stabilizes against such ;*^^ The insecticides DDT, pyrethrin, and naphthal
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Nervous Systems 781 The plasma membrane is lipoprotein, as indicated by much indirect evi- dence. Certain electrochemical properties of the lipoprotein membrane seem to be imparted by a substance that is a quaternary ammonium base, the synthesis of which requires sodium.^"^ Specific aromatic hydrocarbons and other non-polar molecules depolarize, apparently by adsorbing on receptor areas of less than 8 'A;~ calcium stabilizes against such ;*^^ The insecticides DDT, pyrethrin, and naphthalene have non-polar groups which are very active in reducing membrane stability.^-'' Acetylcholine (ACh) is involved in neuro-transmission in one or more unknown ways. It is normally bound, presumably to protein, and may be released in excitation. However, the distribution of acetylcholine is not well correlated with nervous function (see Table 77), and its high con- centration in such organs as spleen and placenta can hardly be connected. A B Fig. 295. Types of cholinesterase. Enzyme from, A, hum,an serum, B, squid ganglion, and C, nucleus caudatus (beef), h, Activity of enzyme; pS, negative log molar concen- tration of substrate. Substrates: Ach, acetylcholine; PrCh, propionylcholine; BuCh, butyrylcholine; TA, triacetin. Modified from Augustinson.^ with propagation. The lowest concentrations of ACh are in those parts of the nervous system which are most sensitive to asphyxia and several bits of evidence suggest that it may be involved in some oxidative system.^-^ An- other hypothesis is that ACh is important in determining permeability and that liberated ACh makes the membrane permeable to potassium and so- dium.^"^^ This hypothesis is supported by evidence regarding permeability of nerve and red blood cells. A third hypothesis^'^ is based on the fact that ACh has a powerful electrochemical action at certain oil-saline interfaces and sug- gests that released ACh may cause
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