Open AccessEffects of Mercuric Chloride and Methyl Mercury on Cholinergic Neuromuscular Transmission in the Guinea‐Pig Ileum
Author(s) -
Candura Stefano M.,
D'Agostino Gianluigi,
Castoldi Anna F.,
Messori Eliana,
Liuzzi Maddalena,
Manzo Luigi,
Tonini Marcello
Publication year - 1997
Publication title -
pharmacology & toxicology
Language(s) - English
Resource type - Journals
eISSN - 1600-0773
pISSN - 0901-9928
DOI - 10.1111/j.1600-0773.1997.tb01963.x
Subject(s) - myenteric plexus , acetylcholine , cholinergic , chemistry , medicine , endocrinology , neuromuscular transmission , ileum , choline , contractility , muscle contraction , tetrodotoxin , guinea pig , calcium , biology , immunohistochemistry
The effects of mercuric chloride (HgCl 2 ) and methyl mercury (MeHg) were examined on basal mechanical activity and electrically‐induced neurogenic cholinergic contractions (twitch contractions) in longitudinal muscle‐myenteric plexus strips from guinea‐pig distal ileum. Both compounds at 0.3‐3 μM slightly enhanced the amplitude of twitch contractions in ~50% preparations. This effect was probably due to facilitation of acetylcholine (ACh) release since 0.1 and 1 μM mercurials increased electrically‐evoked tritium outflow from [ 3 H]choline preloaded muscle layer with attached myenteric plexus. Conversely, higher mercury concentrations inhibited twitch contractions (HgCl 2 IC 50 =21.3±6.4 μM; MeHg IC 50 =45.1±5.5 μM), as well as contractions to exogenous ACh (0.1 μM) in resting preparations, and concomitantly increased the basal tone. The former effects possibly reflected an antimuscarinic activity of mercury, while the latter was related to alterations of calcium homeostasis in the effector cells. Indeed, the effect of HgCl 2 on basal tone was antagonized by the Ca 2+ entry blocker nifedipine (3, 10, 30 nM), indicating Hg‐induced facilitation of Ca 2+ influx through voltage‐dependent channels. On the whole, our results suggest that cholinergic neuromuscular transmission and Ca 2+ ‐dependent mechanisms underlying smooth muscle contractility are targets for mercury toxicity in the intestine.