Zinc ions are endogenous modulators of neurotransmitter‐stimulated capacitative Ca²⁺ entry in both cultured and in situ mouse astrocytes

Abstract

Astrocytes express a variety of metabotropic receptors and their activation leads to a biphasic Ca2+ response due to Ca2+ release from intracellular stores and subsequent capacitative Ca2+ entry. We performed Ca2+ imaging with Fura-2 on cultured mouse astrocytes and showed that extracellular zinc reversibly blocks the capacitative Ca2+ entry following application of the metabotropic ligands ATP, glutamate and endothelin-1. Zinc blocked the plateau phase of the ligand-triggered Ca2+ responses. When ligands were repetitively applied in the presence of zinc the calcium responses progressively decayed and even disappeared, indicating that capacitative Ca2+ entry is required to refill the stores. Zinc inhibited the capacitative Ca2+ entry with a K(i) of approximately 6 microM, which is well within the physiological concentration range of zinc found in the brain. Application of the reducing agent DTT prevented the blocking effect by zinc ions but not the inhibition elicited by the nonphysiological metal ions Gd3+ and La3+, indicating that zinc has a distinct binding site. To monitor the capacitative Ca2+ entry in astrocytes in situ and to determine the effect of zinc on this pathway we utilized X-rhod-1 imaging in hippocampal slices of a transgenic mouse line with green fluorescent astrocytes. Zinc affected the repetitive metabotropic Ca2+ response in the following fashion: (i) after depleting stores in Ca(2+)-free solution, re-addition of Ca2+ led to an influx of Ca2+ via a zinc-sensitive Ca2+ entry route; (ii) with repetitive application of metabotropic ligands, Ca2+ responses became smaller and even disappeared in the presence of zinc. We conclude that zinc, which is co-released from glutamatergic synaptic vesicles upon neuronal activity, has a major impact on shaping the astrocytic calcium responses.

Transcriptional Response ofEscherichia colito TPEN

“…In this study, cDNA microarrays were used to probe the transcriptional response of E. coli to stress by N, N, NЈ, NЈ-tetrakis (2-pyridylmethyl)ethylenediamine (TPEN). TPEN (58,81), a cell-permeative, divalent metal chelator, is often called "Zn(II) specific" (17,33,38,48,59,64,71,79,80,83,88). Our data show significant changes in the transcription of several genes in cells stressed with TPEN.…”

“…In order to probe whether the changes observed in cells grown in the presence of TPEN were due to the chelator, RT-PCR was used to probe for the expression levels of yodA in E. coli cells grown in minimal medium containing 5 M TPEN and 30 M Zn(II). There was no change in transcript levels of yodA when E. coli was cultured in this medium.Despite the fact that TPEN is often referred to as a Zn(II)-specific chelator (17,33,38,48,59,64,71,79,80,83,88), the analyses of our microarray data suggest that the levels of other metal ions may have been affected by the presence of TPEN. …”

“…Despite the fact that TPEN is often referred to as a Zn(II)-specific chelator (17,33,38,48,59,64,71,79,80,83,88), the analyses of our microarray data suggest that the levels of other metal ions may have been affected by the presence of TPEN.…”

Developmental profile and mechanisms of GABA‐induced calcium signaling in hippocampal astrocytes

“…Upon re-perfusion with calciumcontaining saline, both signals recovered only slowly; their amplitudes amounted to roughly 50% of control values after about 20 min (n 5 4; not shown). These results indicate that intracellular calcium stores of astrocytes in acute tissue slices-in contrast to astrocytes in primary culture-are quickly depleted in the absence of extracellular calcium, and are only slowly refilled upon readdition of external calcium, an observation also made by Kresse et al (2005). Moreover, the results suggest that baclofen couples to the same intracellular compartment as t-ACPD and thus might mediate the release of calcium from IP 3 -sensitive intracellular calcium stores following activation of PLC.…”

Role of zinc influx via AMPA/kainate receptor activation in metabotropic glutamate receptor‐mediated calcium release

“…Estimates after tetanic stimulation range between 10-100 lM (Vogt et al, 2000;Li et al, 2001a), even up to 300 lM under extreme conditions (Assaf and Chung, 1984). It is possible that the release from mossy fibers leads to cross talk between extracellular free zinc and calcium via calcium channels such as VDCC (Takeda et al, 2003(Takeda et al, , 2004Cohen-Kfir et al, 2005;Kresse et al, 2005;Minami et al, 2006). Furthermore, zinc released from mossy fibers may be taken up into postsynaptic CA3 pyramidal cells (Howell et al, 1984;Li et al, 2001b).…”