Adenosine A2 receptor activation facilitates 45Ca2+ uptake by rat brain synaptosomes

Area of Science:

• Neuroscience
• Pharmacology
• Cell Biology

Background:

• Adenosine modulates neurotransmitter release via adenosine receptors.
• Adenosine A2 receptor stimulation is linked to increased neurotransmitter release, likely involving calcium influx into presynaptic terminals.

Purpose of the Study:

• To investigate the role of adenosine receptors, specifically A2 receptors, in regulating calcium (Ca2+) uptake into rat brain synaptosomes.
• To determine the specific calcium channel subtypes involved in adenosine-mediated Ca2+ influx.

Main Methods:

• Measurement of 45Ca2+ uptake into rat brain synaptosomes stimulated by veratridine.
• Utilized selective adenosine receptor agonists and antagonists (e.g., 2-chloroadenosine, DPCPX, CGS 21680, DPMA, DMPX).
• Employed specific calcium channel blockers, including omega-agatoxin-IVA (P-type), nifedipine (L-type), and omega-conotoxin GVIA (N-type).

Main Results:

• The mixed adenosine A1/A2 agonist 2-chloroadenosine initially decreased Ca2+ uptake, but increased it when A1 receptors were blocked.
• This A2-mediated increase in Ca2+ uptake was specifically blocked by the P-type calcium channel antagonist omega-agatoxin-IVA.
• Selective A2 receptor agonists (DPMA) increased veratridine-induced Ca2+ uptake, an effect antagonized by DMPX.

Conclusions:

• Activation of adenosine A2 receptors stimulates Ca2+ uptake in depolarized synaptosomes.
• This Ca2+ influx is primarily mediated by P-type calcium channels.
• The findings support the hypothesis that adenosine A2 receptor activation enhances neurotransmitter release through increased intracellular calcium levels.