Glutamate transporter blockade affects Ca(2+) responses in astrocytes

Area of Science:

• Neuroscience
• Cell Biology
• Astrocytes

Background:

• Astrocytes play a crucial role in regulating extracellular glutamate levels.
• Glutamate transporter malfunction leads to increased extracellular glutamate.
• Previous studies showed glutamate pretreatment enhances astrocyte calcium responses.

Purpose of the Study:

• To investigate the effect of glutamate pretreatment on astrocyte calcium responses when glutamate transporter activity is blocked.
• To test the hypothesis that blocking glutamate transport would further elevate calcium responses after glutamate pretreatment.

Main Methods:

• Primary rat astrocyte cultures were pretreated with glutamate and a glutamate transport inhibitor (TBHA) or glutamate in Na+-free solution.
• Calcium (Ca2+) responses were measured following depolarization to evoke voltage-gated Ca2+ currents.
• Experiments were conducted on single astrocytes and astrocyte pairs.

Main Results:

• Glutamate pretreatment under blocked transport conditions paradoxically attenuated Ca2+ transients.
• Faster rise and decay times of Ca2+ transients were observed.
• In astrocyte pairs, attenuated Ca2+ responses were seen in adjoining cells compared to depolarized cells, contrasting previous findings.

Conclusions:

• Extracellular glutamate concentration-dependent regulation of Ca2+ signaling occurs in astrocytes.
• Attenuated Ca2+ responses suggest decreased vesicular release of glutamate and ATP.
• This mechanism may be vital for managing neurotoxic glutamate accumulation in synaptic spaces.