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Divalent heavy metal cations block the TRPV1 Ca(2+) channel.

ABSTRACT: Transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel involved in pain sensation and in a wide range of non-pain-related physiological and pathological conditions. The aim of the present study was to explore the effects of selected heavy metal cations on the function of TRPV1. The cations ranked in the following sequence of pore-blocking activity: Co(2+) [half-maximal inhibitory concentration (IC(50)) = 13 μM] > Cd(2+) (I (50) = 38 μM) > Ni(2+) (IC(50) = 62 μM) > Cu(2+) (IC(50) = 200 μM). Zn(2+) proved to be a weak (IC(50) = 27 μM) and only partial inhibitor of the channel function, whereas Mg(2+), Mn(2+) and La(3+) did not exhibit any substantial effect. Co(2+), the most potent channel blocker, was able not only to compete with Ca(2+) but also to pass with it through the open channel of TRPV1. In response to heat activation or vanilloid treatment, Co(2+) accumulation was verified in TRPV1-transfected cell lines and in the TRPV1+ dorsal root ganglion neurons. The inhibitory effect was also demonstrated in vivo. Co(2+) applied together with vanilloid agonists attenuated the nocifensive eye wipe response in mice. Different rat TRPV1 pore point mutants (Y627W, N628W, D646N and E651W) were created that can validate the binding site of previously used channel blockers in agonist-evoked (45)Ca(2+) influx assays in cells expressing TRPV1. The IC(50) of Co(2+) on these point mutants were determined to be reasonably comparable to those on the wild type, which suggests that divalent cations passing through the TRPV1 channel use the same negatively charged amino acids as Ca(2+).

SUBMITTER: Pecze L

PROVIDER: S-EPMC3566393 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Among the best-studied interactions between soil phagocytic predators and a human-pathogenic fungus is that of Acanthamoeba castellanii and Cryptococcus neoformans The experimental conditions used in amoeba-fungus confrontation assays can have major effects on whether the fungus or the protozoan is ascendant in the interaction. In the presence of Mg2+ and Ca2+ in phosphate-buffered saline (PBS), C. neoformans was consistently killed when incubated with A. castellaniiA. castellanii survived better in the presence of Mg2+ and Ca2+, even when incubated with C. neoformans In the absence of Mg2+ and Ca2+, C. neoformans survived when incubated with A. castellanii, and the percentage of dead amoebae was higher than when incubated without yeast cells. These results show that the presence of Mg2+ and Ca2+ can make a decisive contribution toward tilting the outcome of the interaction in favor of the amoeba. Of the two metals, Mg2+ had a stronger effect than Ca2+ The cations enhanced A. castellanii activity against C. neoformans via enhanced phagocytosis, which is the major mechanism by which amoebae kill fungal cells. We found no evidence that amoebae use extracellular killing mechanisms in their interactions with C. neoformans In summary, the presence of Mg2+ and Ca2+ enhanced the cell adhesion on the surfaces and the motility of the amoeba, thus increasing the chance for contact with C. neoformans and the frequency of phagocytosis. Our findings imply that the divalent cation concentration in soils could be an important variable for whether amoebae can control C. neoformans in the environment.IMPORTANCE The grazing of soil organisms by phagocytic predators such as amoebae is thought to select for traits that enable some of them to acquire the capacity for virulence in animals. Consequently, knowledge about the interactions between amoebae and soil microbes, such as pathogenic fungi, is important for understanding how virulence can emerge. We show that the interaction between an amoeba and the pathogenic fungus C. neoformans is influenced by the presence in the assay of magnesium and calcium, which potentiate amoebae. The results may also have practical applications, since enriching soils with divalent cations may reduce C. neoformans numbers in contaminated soils.

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Divalent heavy metal cations block the TRPV1 Ca(2+) channel.

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