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At least 649 records · Page 36Linked to original sources
PubMed1978

Effects of divalent cations, lanthanum, cation chelators and an ionophore on acetylcholine antinociception.

The antinociceptive effect of intracerebroventricularly administered acetylcholine as measured in the mouse tail-flick test was reduced by intracerebroventricularly injected calcium, magnesium and manganese. Maximum antagonism of acetylcholine-induced antinociception was observed with a 1-hour calcium pretreatment. Significant reduction existed at 2- but not 4-hour pretreatment. Barium and strontium were inactive. The antinociceptive effect of acetylcholine was potentiated by lanthanum and ethylene glycol tetraacetic acid but not by ethylenediamine tetraacetic acid. The ionophore A23187 was shown to increase greatly the antagonistic effect of a low dose of calcium. The ionophore alone did not significantly alter the effect of acetylcholine. Thus, it appears that calcium must penetrate cell membranes to reduce the effect of acetylcholine. In addition to acetylcholine, it was found that the antinociceptive effects of oxotremorine and physostigmine could also be reduced by calcium. These data indicate that alterations in intracellular calcium are involved in cholinergically induced antinociception.

Acetylcholine↗
PubMed1986

Conformational changes induced by binding of divalent cations to calregulin.

Scatchard analysis of equilibrium dialysis studies have revealed that in the presence of 3.0 mM MgCl2 and 150 mM KCl, calregulin has a single binding site for Ca2+ with an apparent dissociation constant (apparent Kd) of 0.05 microM and 14 binding sites for Zn2+ with apparent Kd(Zn2+) of 310 microM. Ca2+ binding to calregulin induces a 5% increase in the intensity of intrinsic fluorescence and a 2-3-nm blue shift in emission maximum. Zn2+ binding to calregulin causes a dose-dependent increase of about 250% in its intrinsic fluorescence intensity and a red shift in the emission maximum of about 11 nm. Half-maximal wavelength shift occurs at 0.4 mol of Zn2+/mol of calregulin, and 100% of the wavelength shift is complete at 2 mol of Zn2+/mol of calregulin. In the presence of Zn2+ and calregulin the fluorescence intensity of the hydrophobic fluorescent probe 8-anilino-1-napthalenesulfonate (ANS) was enhanced 300-400% with a shift in emission maximum from 500 to 480 nm. Half-maximal Zn2+-induced shift in ANS emission maximum occurred at 1.2 mol of Zn2+/mol of calregulin, and 100% of this shift occurred at 6 mol of Zn2+/mol of calregulin. Of 12 cations tested, only Zn2+ and Ca2+ produced changes in calregulin intrinsic fluorescence, and none of these metal ions could inhibit the Zn2+-induced red shift in intrinsic fluorescence emission maximum. Furthermore, none of these cations could inhibit or mimic the Zn2+-induced blue shift in ANS emission maximum. These results suggest that calregulin contains distinct and specific ligand-binding sites for Ca2+ and Zn2+. While Ca2+ binding results in the movement of tryptophan away from the solvent, Zn2+ causes a movement of tryptophan into the solvent and the exposure of a domain with considerable hydrophobic character.

Animals↗
PubMedDate not supplied

Influence of divalent cations on rabbit atria and modification of catecholamine response on pacemaker cells.

Spontaneously beating isolated atria of rabbits responded to Mn++ and Co++ with a progressively increasing negative chronotropism and inotropism, which was reversible by washout and by elevating the bath concentration of Ca++. The cumulative dose response curve for adrenaline for chronotropic response was markedly shifted to the right in the presence of Mn++ or Co++. This effect was also reversible. Verapamil produced only a moderate decline in spontaneous rate and contractility and did not block the chronotropic response to adrenaline. It is concluded that Mn++ and Co++ block the action of catecholamine on the pacemaker cells and they differ at least in part from organic calcium channel antagonists in their mechanism of action.

Animals↗
PubMed1985

Methanogenesis and the K+ transport system are activated by divalent cations in ammonia-treated cells of Methanospirillum hungatei.

We describe a K+ transport system in Methanospirillum hungatei cells depleted of cytoplasmic K+ via an ammonia/K+ exchange reaction (Sprott, G. D., Shaw, K. M., and Jarrell, K. F. (1984) J. Biol. Chem. 259, 12602-12608). Ammonia-treated cells contained low concentrations of ATP and were unable to make CH4 or to transport 86Rb+. All of these properties were restored by CaCl2, MgCl2, or MnCl2, and not by CoCl2 or NiCl2. The Rb+ transport system had a Km of 0.42 and Vmax of 29 nmol/min X mg; K+ inhibited competitively. Both H2 and CO2 were required for appreciable transport, whereas air, valinomycin, or nigericin were potent inhibitors. The influx of Rb+ was electrogenic and associated with proton efflux, producing a delta pH (alkaline inside) in acidic media. In the absence of K+ (or Rb+), the activation of CH4 synthesis by Mg2+ produced little change in the cytoplasmic pH, showing that methanogenesis did not elicit a net efflux of protons. The pH optimum for transport was in the range 6.0-7.3 where the transmembrane pH gradient would contribute minimally to the proton motive force. Protonophores at pH 6.3 caused a partial decline in CH4 synthesis and the ATP content and dramatically collapsed Rb+ transport. These and other inhibitor experiments, coupled with the fact that the Rb+ gradient was too large to be in equilibrium with the proton motive force alone, suggest a role for both ATP and the proton motive force in Rb+ transport. Also, a role for K+ in osmoregulation is indicated.

Ammonia↗