Ca(2+)-dependent release from rat brain of cannabinoid receptor binding activity

Area of Science:

• Neuroscience
• Pharmacology
• Molecular Biology

Background:

• The identification of cannabinoid receptors in the central nervous system (CNS) suggests the existence of an endogenous ligand.
• Neuromodulators are often stored in intracellular vesicles and released upon stimulation.

Purpose of the Study:

• To investigate the hypothesis of an endogenous ligand for cannabinoid receptors.
• To determine if increased intracellular calcium levels can stimulate the release of cannabinoid-binding activity.

Main Methods:

• Utilized the Ca2+ ionophore A23187 to stimulate release of cannabinoid-like activity.
• Measured the concentration-dependent release of binding activity in response to varying extracellular Ca2+ levels.
• Assessed the ability of released activity to displace [3H]CP-55940 binding to cannabinoid receptors in rat synaptosomal membranes.

Main Results:

• The Ca2+ ionophore A23187 induced the release of cannabinoid-like binding activity specifically in the presence of Ca2+.
• Release was observed when extracellular free Ca2+ exceeded 60 nM, with maximal effect at 1.2 microM A23187, consistent with vesicular release.
• The released substance demonstrated concentration-dependent displacement of [3H]CP-55940 binding, confirming its interaction with cannabinoid receptors.

Conclusions:

• This study reports the first evidence of an endogenous brain substance that binds to cannabinoid receptors.
• The release of this substance is dependent on extracellular calcium, supporting its role as a Ca2+-dependent neuromodulator.
• These findings open new avenues for understanding the endocannabinoid system and its regulation.