Modification of the Mechanical Response of the Smooth Muscles of Pregnant Mouse Myometrium and Guinea Pig Ileum by Cadmium and Manganese Ions

Abstract

Summary Effects of divalent cations on pregnant mouse myometrium and guinea pig ileum were investigated by recording electrical and mechanical activities. 1. Application of transition metal cations (Mn, Cd, Co, Ni, and Zn) inhibited the spontaneous activities of mouse myometrium. Except for Mn, treatment with these cations in a concentration of 1 mM and for 1-2 min caused an irreversible suppression of the mechanical response. 2. Myometrial membrane was hyperpolarized with 0.5 mM Cd decreasing membrane resistance. During application, contractures induced by excess K or carbachol was inhibited. After treatment with 0.5-1 mM Cd for 1-2 min, electrical and mechanical activities dissociated, i.e. spike activity resumed but mechanical activity was suppressed. The membrane was depolarized by carbachol to the control value, but contraction did not developed. 3. By contrast, contracture of mouse myometrium induced by excess K or carbachol application were potentiated after treatment with Mn. 4. The effects of divalent cations on guinea pig ileum were essentially the same as with mouse myometrium, i.e. treatment with Mn potentiated mechanical response whereas other ions caused irreversible suppression.In the mammalian myocardium, polyvalent cations such as Ni, Co, and Mn ions commonly depress Ca conductivity, while leaving the fast transient Na current only slightly affected (KAUFMANN and FLECKENSTEIN, 1965;OCHI, 1970;KOHLHARDT et al., 1973). This may lead to a decreased Ca influx into the depolarized myocardial cell so that decoupling of excitation-contraction mechanism occurs as in simple Ca-deficient media. A recent report on the rabbit atrium indicates that Cd induces a marked depression of the action potential. In addition, the contractile force-rate curve is significantly depressed by the ion (TODA,

Effects of calcium and manganese ions on mechanical properties of intact and skinned muscles from the guinea‐pig stomach

“…MnCl2 also possessed multiple actions on the mechanical response of smooth muscle cells of the antrum, namely, this agent suppressed the spontaneous contraction, suppressed the Ca-induced contraction evoked by application of Ca in the Ca-free solution in polarized and depolarized muscles, and prevented the leakage ofCa from the store site, under conditions ofCa-free solution. It was also reported that MnCl2 modifies the Ca influx and penetrates the cell, thus causing either a suppression (Keene, Seidel & Bohr, 1972;Katase & Tomita, 1972;Osa, 1974;Yoshida et al 1977) or an acceleration of the mechanical responses (Shibata, 1969;Ogasawara et al 1980) Fig. 8A, the amplitude of the 10mM-Mn (8 mm free Mn)-induced contraction was much smaller than the contraction evoked by 1 x 10-6 M-Ca and such may in part be due to a reduction in the Mg-ATP concentration with production of the Mn-ATP complex.…”

“…MnCl2 suppressed the Ca spike in visceral smooth muscles (Brading et al 1969;Osa, 1974;. MnCl2 also possessed multiple actions on the mechanical response of smooth muscle cells of the antrum, namely, this agent suppressed the spontaneous contraction, suppressed the Ca-induced contraction evoked by application of Ca in the Ca-free solution in polarized and depolarized muscles, and prevented the leakage ofCa from the store site, under conditions ofCa-free solution.…”

“…The effects of MnCl2 on the stomach smooth muscle were also investigated in comparison to the effects of Ca on mechanical properties. Mn is known to inhibit the spike generation and either accelerates or inhibits the contraction in smooth and cardiac muscles (Brading, Bulbring & Tomita, 1969;Imai & Takeda, 1967;Osa, 1974;Ochi, 1976; Yoshida, Taniyama, Araki & Matsumoto, 1977;Chapman & Ellis, 1977;Ogasawara, Kato & Osa, 1980;Coraboeuf, Gautier & Guiraudou, 1981).…”

Effects of porcine relaxin on contraction, membrane response and cyclic AMP content in rat myometrium in comparison with the effects of isoprenaline and forskolin

“…On the other hand, the enhancement of f-adrenoceptor inhibition by Mg application via an intracellular process has been proposed in some smooth muscle tissues (myometrium, Maruta & Osa, 1989; taenia, Bolton, 1979;Weiss, 1981). Yet its action on contraction is complicated, and is not fully understood; MnCl2 modifies the Ca influx and penetrates the cell, thus causing either a suppression (Keene et al, 1972) or an acceleration (Shibata, 1969;Osa, 1974;Sakai & Uchida, 1981;Itoh et al, 1982;Lategan & Brading, 1988) of the mechanical responses in various visceral muscles. Intracellular accumulation of Mn was experimentally proved to occur in rat ventricular muscle, in which the baseline tension was gradually elevated when exposed to 0.2mm Mn (Chapman & Ellis, 1977).…”

Effects of noradrenaline and acetylcholine on electro‐mechanical properties of the guinea‐pig portal vein

“…MnCI2 inhibits the spike generation and produces either a suppression (Keene et al, 1972;Katase & Tomita, 1972;Osa, 1974;Yoshida et al, 1977) or an acceleration of the mechanical responses (Shibata, 1969;Ogasawara et al, 1980). In the guinea-pig portal vein, MnCl2 inhibited the Ca-spike and Ca influxes in polarized and depolarized membranes, thus suppressing the contraction, while MnCl2 may suppress the leakage of Ca from storage sites after re-addition of Ca to the Ca-free solution and enhance the contraction evoked by either caffeine or NA.…”