Effect of eserine on the chick biventer cervicis preparation

1. The relationship between the capacity of the chick biventer preparation, both intact tissue and homogenate, to inactivate acetylcholine and the ability of eserine to increase the sensitivity of the tissue to acetylcholine have been investigated.2. At concentrations of eserine of 2.69 x 10(-9)M and 2.69 x 10(-8)M the capacity of the whole tissue to inactivate acetylcholine is reduced by 5% and 15% respectively. These concentrations of eserine increase the sensitivity of the preparation to acetylcholine by factors of 2 and 4 respectively, without a change of slope in regression lines.3. At concentrations of eserine of 2.69 x 10(-7)M and 2.69 x 10(-6)M the capacity of the whole tissue to inactivate acetylcholine is reduced by 40% and 80% respectively, and the sensitivity to acetylcholine increased by factors of 70 and 800 respectively, along with marked increases in the slopes of the regression lines.4. An attempt has been made to quantify these differences by proposing a model in which cholinesterase in the tissue is regarded as a network, preventing the access of a large fraction of the acetylcholine to its site of action.5. It is suggested that, whereas the increase in sensitivity to acetylcholine at eserine concentrations of 2.69 x 10(-9)M and 2.69 x 10(-8)M can be interpreted as an anticholinesterase effect (which is still present at higher concentrations), that seen at the higher concentrations may represent a direct action of eserine on the tissue.6. It is further suggested that there are barriers to penetration in intact tissue to both substrate and inhibitor, which invalidate attempts to extrapolate results from homogenates.