Influence of acetyl- -methylcholine, carbamoylcholine, and bis-pyridinium compounds on the activity of acetylcholinesterase

Characterization of cholinesterase of muscularis muscle of Bufo marinus

We have characterized the cholinesterase (ChE) of muscularis muscle of Bufo marinus by selectively using specific inhibitors of acetylcholinesterase and pseudocholinesterase and observing susceptibility to inhibition when substrate is present in excess. The ChE activity in this preparation due to acetylcholinesterase (AChE) and pseudocholinesterase (BuChE) was 90 and 10%, respectively. The optimum temperature and pH for the ChE were 38 degrees C and 7.4, respectively and the excess substrate inhibition was noted above a pS of 2.6. The Km for acetylthiocholine (ASCh) was 0.76 X 10(-4) M.

Intracellular injection of acetylcholine blocks various potassium conductances in vagal motoneurons

Injection of acetylcholine into cholinergic neurons of the dorsal motor nucleus of the vagus induced membrane depolarization, an increase in input resistance, a decrease of early and late afterhyperpolarizations and a prolongation of the action potential. These effects were reversible and within 10-20 min almost complete recovery was always observed. Externally applied acetylcholine, even with doses as high as 15 mM, was not effective. Acetylcholine appeared to block voltage- and Ca2+-dependent K+ conductances. This block was manifested by the reduction of both the early and late afterhyperpolarizations and a decrease of the delayed rectification. The reversal potential for the conductance decrease was 15-30 mV negative to the resting potential. As a result of this blockade an increased Ca2+ current ensues, which is responsible for most of the prolongation of the action potential. The same responses were obtained after the injection of carbamylcholine, neostigmine and choline. However, unlike acetylcholine no sign of recovery was observed. In fact injection of neostigmine, carbamylcholine or neostigmine, together with acetylcholine, produced a delayed response which may reflect the accumulation of endogenous acetylcholine.

Cholinomimetic teratogens. V. The effect of oximes and related cholinesterase reactivators

Pyridine-2-aldoxime methiodide and pyridine-2-aldoxime methyl methane sulfonate (P2S) used as supplements to carbachol or neostigmine, greatly lowered the incidence of chicken embryos of vertebral defects and muscular hypoplasia. With 4-pyridine aldoxime the effect of the teratogens was less reduced. Supplementation of carbachol or neostigmine with either ambenonium or toxogonin lessened the occurrence of muscular hypoplasia, but did little, if anything, to prevent malformation of the neck vertebrae. In tests with physostigmine P2S as supplement reduced or prevented cervical defects, but failed to protect the nicotinamide-sensitive parts of the embryo.