Chemical events in conducting and synaptic membranes during electrical activity

A comparison of the potency of newly developed oximes (K005, K027, K033, K048) and currently used oximes (pralidoxime, obidoxime, HI-6) to reactivate sarin-inhibited rat brain acetylcholinesterase by in vitro methods

The potency of newly developed and currently used oximes to reactivate sarin-inhibited acetylcholinesterase was evaluated using in vitro methods. A rat brain homogenate was used as a source of acetylcholinesterase. Significant differences in reactivation potency among all tested oximes were observed. Although the ability of newly developed oximes to reactivate sarin-inhibited acetylcholinesterase does not reach the reactivating potency of the oxime HI-6, the oxime K033 seems to be a more efficacious reactivator of sarin-inhibited acetylcholinesterase than other currently available oximes (pralidoxime, obidoxime) at concentrations (10(-5)-10(-4)M) corresponding to recommended doses in vivo. The results of our study also confirm that the reactivation potency of the tested reactivators depends on many factors, such as (1) the number of pyridinium rings, (2) the number of oxime groups and their position, and (3) the length and the shape of the linkage bridge between pyridinium rings.

Non-synaptic cholinergic modulation of neurogenic twitches of the guinea-pig ileum

The effect of cholinergic and anticholinergic compounds on conduction of neuronal excitation has been studied in myenteric plexus-longitudinal muscle strips from the guinea-pig ileum. A preparation in a special triple bath was drawn through two rubber membranes dividing the strip into three segments. Neurogenic stimulation of the oral segment set up nerve action potentials propagating aborally across the middle segment (10 mm) so that the aboral segment might be also invaded, eventually. Drugs were added to the middle segment to affect neuronal propagation (non-synaptic effects) which was monitored by twitch height of the aboral segment. The application of acetylcholine to the middle segment augmented aboral twitches. The effects of nicotine, pilocarpine and oxotremorine were selectively blocked by (+)-tubocurarine, pirenzepine and atropine, respectively. The effect of acetylcholine was suppressed by pirenzepine and atropine and mimicked by doubling of KCl concentration. The effect of acetylcholine may be thus explained by the facilitated propagation of nerve action potentials in partially depolarized cholinergic terminals via stimulation of muscarinic receptors. The adenylate cyclase system is not directly involved in the mechanism of muscarinic facilitation of neuronal propagation in the terminals; however, it may participate in the modulation of a final common effector mechanism.

The distribution of acetylcholinesterase in buds of the rat vallate papilla as determined by electron microscope histochemistry

The distribution of acetylcholinesterase (AChE) in the rat vallate papillary bud was investigated by histochemical electron microscopy. Previous reports of specific AChE activity around subgemmal and intragemmal nerves and between some taste bud cells have been confirmed. In addition we have consistently observed dense precipitation between microvilli in the taste pore. The studies suggest that the neurotransmitter, acetylcholine, may be involved in early events in the taste process which are believed to occur in the pore.

Temperature and pressure adaptation of the binding site of acetylcholinesterase

1. Studies with a carbon substrate analogue, 3,3-dimethylbutyl acetate, indicate that the hydrophobic contribution to binding at the anionic site of acetylcholinesterase is strongly disrupted at low temperatures and high pressures. 2. Animals living in different physical environments circumvent this problem by adjusting the enthalpic and entropic contributions to binding. 3. An extreme example of this adaptational strategy is supplied by brain acetylcholinesterase extracted from an abyssal fish living at 2 degrees C and up to several hundred atmospheres of pressure. This acetylcholinesterase appears to have a smaller hydrophobic binding region in the anionic site, playing a measurably decreased role in ligand binding.

An attempt at an integral interpretation of nerve excitability

A qualitatively consistent integral interpretation of biochemical, electrophysiological, and biophysical data on nerve activity is given in terms of a basic excitation unit. This operational term models a dynamically coupled assembly of membrane components accounting for graded and all-or-none responses upon stimulation. The analysis contains a series of suggestions linking controversial interpretations and is aimed at stimulation of experimental studies providing the basis for a quantitative integral theory of nerve excitation.