Effects of methylmercuric chloride and bis (methylmercuric) selenide on responses of isolated intestinal smooth muscle of the guinea-pig.

Abstract

The neurologically toxic substance, methylmercury, is detoxicated by simultaneous application of selenite. In vivo formation of bis (methylmercuric) selenide has been suggested as the mechanism of detoxication by selenite. By using isolated guinea-pig taenia coli preparations, the effects of methylmercuric chloride and bis (methylmercuric) selenide on contractile responses to nerve and direct stimulation were investigated. Application of either drugs scarcely affected contractile responses to direct stimulation. However, contractile responses to nerve stimulation were severely reduced by methylmercuric chloride. The effect of bis (methylmercuric) selenide was considerably weaker than methylmercuric chloride. The site blocked by methylmercuric chloride and bis (methylmercuric) selenide in the taenia preparation was discussed methylmercuric chloride (MMC) ; bis ( methylmercuric ) selenide (BMS) ; guinea-pig taenia coli

Inhibitory effect of methylmercuric chloride on the contraction mediated by muscarinic receptor of intestinal smooth muscle of the guinea-pig.

“…4). In our previous study MMC did little affect the mechanical response to direct stimulation in the smooth muscle cells (Fukushi and Yamamoto 1985). Therefore, the present and previous findings suggest that MMC causes a blockage of nerve-muscle transmission not by interfering with nerve excitation or transmitter release but by interfering with activation of muscarinic receptor on the smooth muscle membrane of the taenia coll.…”

“…By treatment with MMC, both contractions evoked by the transmural stimulation and nicotine were markedly suppressed in magnitude. The response to transmural stimulation was 27+11% (n=5-7) of the control at 5 min after exposure to MMC and waned to a null at 15 min (see Fukushi and Yamamoto, 1985). In contrast, a contraction evoked by a direct stimulation of muscle cells (2 V/cm, 50 Hz) was little affected by MMC (Fig.…”

“…Detailed description on the method has already been published (Fukushi and Yamamoto 1985). In brief, a preparation was suspended in a 5 ml bath under 0.2 g tension in a modified Krebs solution at 32-34°C.…”

“…Before starting actual recording all preparations were incubated for 45 min in the control solution containing ethanol at the same concentration as the test solution (except in the study for high-K solution) (see Fukushi and Yamamoto 1985).…”

“…Moreover in the rat brain, MMC inhibits the activity of choline acetyltransf erase (Omata et al 1982) which also may result in a failure of the transmission of impulses. In the smooth musle preparation of the guinea-pig taenia coli, we previously reported that MMC markedly reduced the contractile response evoked by a cholinergic nerve stimulation (Fukushi and Yamamoto, 1985). Since MMC did not change the response of this tissue evoked by a direct electrical stimulation of the smooth muscle, it was considered that MMC might induce the nerve-smooth muscle transmission failure by suppressing some process of excitation-transmitter release coupling of cholinergic nerve fibre and/or by suppressing receptor activation on the smooth muscle membrane.…”