Effects of mercuric ions on isolated guinea-pig ileum

Abstract

The possible physiological significance of low concentrations of Hg2+ in the guinea-pig ileum has been investigated. Responses to nerve stimulation by single electrical shocks, acetylcholine (ACh), and histamine (Hi) and the response to ACh of a depolarized preparation were examined. A stimulant effect of Hg2+, in the concentration range of 10 nM-1 microM, dominated in intestine accommodated in biological saline solution. This excitatory effect was probably mainly due to stimulation of a depolarization-coupled initiation of the contraction. The inhibitory effect of Hg2+, 10 nM-1 microM, observed in depolarized muscle was presumably due to a decreased Ca2+ availability for the contractile process. In the higher concentration range, 1-100 microM, a probably direct action on the contractile elements causing irreversible deterioration of the preparation seems to be present.

Effects of Mercuric Chloride and Methyl Mercury on Cholinergic Neuromuscular Transmission in the Guinea‐Pig Ileum

“…In this regard, nanomolar concentrations of Hg2+ have been found to enhance basal tone and to facilitate electrically-stimulated neurogenic (cholinergic) contractions in the guinea-pig ileum (Moberg 1986). These effects were attributed to stimulation of a depolarization-coupled initiation of the contraction, although a prejunctional action (e.g.…”

“…These effects were attributed to stimulation of a depolarization-coupled initiation of the contraction, although a prejunctional action (e.g. facilitation of acetylcholine release) could not be excluded (Moberg 1986). Apparently, the effects of nanomolar organic Hg concentrations have never been explored.…”

“…Conversely, micromolar concentrations of both inorganic (Moberg 1986;Moberg et al 1991;Abram & Korossy 1994) and organic (Fukushi & Yamamoto 1985;Fukushi & Wakui 1985) Hg have been found to irreversibly inhibit enteric cholinergic contractions. Possible mechanisms underlying this effect include: (i) inhibition of acetylcholine release (Abram & Korossy 1994); (ii) antagonist properties at postjunctional muscarinic receptors (Fukushi & Wakui 1985); (iii) a direct action on the contractile elements (Moberg 1986;Moberg et al 1991).…”

“…Possible mechanisms underlying this effect include: (i) inhibition of acetylcholine release (Abram & Korossy 1994); (ii) antagonist properties at postjunctional muscarinic receptors (Fukushi & Wakui 1985); (iii) a direct action on the contractile elements (Moberg 1986;Moberg et al 1991).…”

“…For this purpose, the effects of submicromolar Hg concentrations on electrically-induced tritiated ACh release were examined together with the effects of mercurials (in the submicromolar and micromolar range) on electrically-or ACh-induced contractions in guinea-pig longitudinal muscle-myenteric plexus preparations. The ionic mechanisms responsible for the enhancement of the intestinal basal tone induced by Hg2+ (see Moberg 1986) were also explored. Preliminary results of this study have been reported earlier in abstract form Castoldi et al 1995).…”