Optical imaging reveals cation--Cl(-) cotransporter-mediated transient rapid decrease in intracellular Cl(-)...

Area of Science:

• Neuroscience
• Cellular Physiology
• Biochemistry

Background:

• Neuronal chloride homeostasis is critical for brain function.
• Ischemia-induced changes in intracellular chloride concentration ([Cl(-)](i)) contribute to neuronal injury.
• The role of specific chloride transporters in ischemic conditions is not fully understood.

Purpose of the Study:

• To investigate the mechanisms underlying transient intracellular chloride decrease during oxygen-glucose deprivation in rat brain slices.
• To identify the specific chloride transporters involved in this phenomenon.
• To explore the potential neuroprotective role of this transient chloride efflux.

Main Methods:

• Real-time intracellular chloride concentration ([Cl(-)](i)) recordings using MEQ fluorescence in rat brain slices.
• Oxygen-glucose deprivation as an in vitro model of ischemia.
• Pharmacological inhibition of chloride transporters (pumps, channels, antiporters, cotransporters).
• Manipulation of ion gradients (Na(+), K(+)) to assess transporter function.
• RT-PCR to identify the specific cotransporter isoform.

Main Results:

• Oxygen-glucose deprivation induced a rapid, transient decrease in [Cl(-)](i), preceding a sustained increase.
• The transient decrease was inhibited by cation-Cl(-) cotransporter inhibitors (bumetanide, furosemide) but not by blockers of other Cl(-) transport mechanisms.
• The Na(+),K(+)-2Cl(-) cotransporter (NKCC1) was identified as the primary mediator of the transient [Cl(-)](i) decrease.
• Inhibition of NKCC1 by reducing the Na(+) driving force prevented the transient chloride efflux.

Conclusions:

• The transient intracellular chloride decrease during ischemia is primarily mediated by rapid inhibition of the inwardly directed Na(+),K(+)-2Cl(-) cotransporter (NKCC1).
• This rapid chloride efflux may serve as a protective mechanism against the detrimental effects of sustained chloride influx during ischemic injury.
• NKCC1 plays a crucial role in regulating neuronal chloride levels under ischemic conditions.