46 II. DIGESTION AND ABSORPTION OF FATS 



tration gradient when the cells were incubated with acetylcholine, and the 

 cholinesterase activity was maintained, provided that the cell had pre- 

 viously lost part of its complement of K+. This reaction could be inhibited 

 by eserine. Replacement of K + in cells during the metabolism of glucose 

 was shown to be blocked in a similar manner by eserine. It is concluded 

 that a single method exists for the replacement of potassium in blood 

 cells, irrespective of whether the substrate is glucose or acetylcholine, and 

 that the mechanism depends upon active cholinesterase. 



An understanding of the relationship of cholinesterase to cell permea- 

 bility has been somewhat extended by the experiments of Taylor, Weller, 

 and Hastings, 262 who used radioactive K + . It was shown that cholinester- 

 ase inhibitors such as eserine and diisopropyl fluorophosphate (DFP) 

 caused a loss of K + from the cells, principally as a result of a decrease in the 

 rate at which K + entered the cells from the plasma. No direct relation- 

 ship was found, however, between the inhibition of cholinesterase activity 

 and potassium leakage from the cell. When choline acetylase inhibitors 

 (methylene blue or 2-methyl-l,4-naphthoquinone) were employed, a loss 

 of K + from the cells was also observed; in this case, however, the increase 

 in the rate at which K + left the cell was responsible for the phenomenon. 

 It is not known whether or not changes in permeability may account for 

 the finding of Robertson et al. 2 * 3 that topical application of acetylcholine 

 to the pyloric mucosa causes gastrin to be released, resulting in stimulation 

 of acid secretion by the fundic glands. Acetylcholine has been reported 

 by McDowall 264 to act as a stimulant to heart muscle. In contradistinc- 

 tion to adrenalin, acetylcholine acts upon the force of the heart rather 

 than upon its frequency. 



(/) Physiological and Pathological Factors Altering the Amount of Cholin- 

 esterases. Age and species have an important effect upon cholinesterase 

 activity. Thus, in newborn humans, rats, rabbits, and cats, the cholin- 

 esterase activity of the serum tended to be near the adult level, but rose 

 shortly after birth to approximately twice that of the adult. 265 McCance 

 et al. 26b reported that the cholinesterase activity of the colostrum of man 

 and of the cat was negligible, but that the level of this enzyme was very 

 high in the colostrum of the bitch. This latter fact may explain why the 



262 1. M. Tavlor, J. M. Weller, and A. B. Hastings, Am. J. Physiol, 168, 658-665 

 (1952). 



263 C. R. Robertson, K. Langlois, C. G. Martin, G. Slezak, and M. I. Grossman, Am. 

 J. Physiol., 163, 27-33 (1950). 



264 R. J. S. McDowall, J. Physiol., 104, 392-403 (1946). 



265 R. A. McCance, A. O. Hutchinson, R. F. A. Dean, and P. E. H. Jones, Biochem. J., 

 45, 493-496(1949). 



