Mechanisms of the inhibition of endplate acetylcholine receptors by antiseptic chlorhexidine (experiments and models)

Abstract

Mechanisms of the inhibition of evoked multiquantal endplate currents (EPC) by chlorhexidine (CHX) were studied in electrophysiological experiments and by mathematical modeling to discriminate between possible channel, receptor, and non-receptor effects of this common antiseptic drug. Experiments were carried out on the isolated neuromuscular preparation of the cut m. sartorius of the frog Rana ridibunda. The nerve-stimulation-evoked endplate currents were measured by standard double microelectrode technique. For the mathematical simulation, a method based on the solution of a system of ordinary differential equations was used. CHX in milimolar concentrations suppressed the amplitude and shortened the evoked EPC. Recovery of the EPC amplitude was very slow, and EPC shortening persisted during 30-40 min washout of the drug. There is no indication that CHX competes for acetylcholine or carbachol binding site(s). A comparison of the experimental data with mathematical simulation made it possible to construct a reliable kinetic scheme, which describes the action of CHX. CHX induces a combined slow blockade of the open ionic channel and long-lasting allosteric inhibition of the nicotinic acetylcholine receptor. The very slow washout of the drug in terms of EPC amplitude and virtually no recovery of the shortened EPC time course might substantiate certain caution to avoid unintentional high-dose application during its antibacterial application.

Lethal and sub lethal effects of the biocide chlorhexidine on aquatic organisms

“…The induction of ChE in fish exposed to chlorhexidine is not fully understood. In mammals and amphibians, chlorhexidine has been shown to affect the nervous system, including nerve degeneration (Röed 1973;Henschen and Olson 1984) and inhibition of nicotinic acetylcholine receptors (Shaihutdinova et al 2009). One could speculate that the inhibition of nicotinic acetylcholine receptors may be related to the enhancement of ChE activity since this would lead to an increase of acetylcholine in the synaptic cleft and, consequently, increase ChE activity in an attempt to promote the degradation of the excess of acetylcholine.…”

“…Moreover, the early stress responses caused by ChD on zebrafish embryos were assessed based on a battery of enzymatic biomarkers from different metabolic pathways Domingues et al (2010). Since ChD affects the nervous system of several organisms (Röed 1973;Henschen and Olson 1984;Shaihutdinova et al 2009) the cholinesterase (ChE) was selected due to its key role in the hydrolysis of acetylcholine in peripheral and central nervous systems (Holth et al 2008). In addition, intending to give a first insight on the oxidative stress effects caused by ChD, the enzyme catalase (CAT), an antioxidant enzyme that acts against reactive oxygen species (ROS) (Oost et al 2003), was also selected.…”