Proton-dependent zinc release from intracellular ligands

Area of Science:

• Neuroscience
• Cellular Biology
• Biochemistry

Background:

• Intracellular pH (pHi) drop in neurons triggers release of zinc (Zn2+) from unknown stores.
• Mitochondria and acidic organelles were initially considered potential sources of Zn2+ release.
• Previous studies lacked identification of specific intracellular ligands responsible for Zn2+ release upon acidification.

Purpose of the Study:

• To identify the specific intracellular stores responsible for releasing Zn2+ during neuronal acidification (pHi 6.6 to 6.1).
• To investigate the role of various intracellular ligands in chelating and releasing Zn2+ under acidic conditions.
• To determine if mitochondria or acidic organelles contribute to acid-induced Zn2+ release.

Main Methods:

• Utilized cultured cortical and hippocampal neurons.
• Employed the protonophore FCCP to inhibit mitochondrial and acidic organelle Zn2+ uptake.
• Investigated acid-induced Zn2+ release from various Zn2+-ligand complexes in vitro using the FuraZin-1 fluorescent probe.
• Assessed Zn2+ release rates from zinc-cysteine and zinc-histidine complexes.

Main Results:

• FCCP treatment did not prevent repeated Zn2+ release, ruling out mitochondria and acidic organelles as primary sources.
• In vitro studies showed that only zinc-cysteine complexes rapidly accelerated Zn2+ release when pH decreased from 6.6 to 6.1.
• Zinc-cysteine complexes also released Zn2+ when treated with a histidine-modifying agent at pH 7.2, further implicating cysteine.

Conclusions:

• Intracellular Zn2+ ligands, specifically cytosolic zinc-cysteine complexes, are the primary stores responsible for acid-induced Zn2+ release in neurons.
• Mitochondria and acidic organelles do not appear to be significant contributors to this phenomenon.
• The findings identify a novel mechanism for regulating intracellular Zn2+ levels during neuronal acidification.