Phosphorylation of membrane proteins at a cholinergic synapse

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Membrane protein kinase activity and substrates exist in Torpedo californica electric organ fractions.
• These fractions are enriched in the acetylcholine receptor.

Purpose of the Study:

• To investigate the role of protein phosphorylation in synaptic events.
• To identify protein kinase activity and substrates associated with acetylcholine receptors.

Main Methods:

• Preparation of membrane fractions from Torpedo californica electric organ.
• Assaying endogenous protein kinase activity and substrate phosphorylation.
• Investigating the effects of potassium (K+) and the cholinergic ligand carbachol on phosphorylation.

Main Results:

• Phosphorylation of four polypeptides was stimulated 9-fold by K+.
• Carbachol inhibited phosphorylation of these polypeptides by 72% under specific ionic conditions (1mM Na+, 100 mM K+).
• The 65,000-dalton component of the acetylcholine receptor appears to be a substrate for the endogenous protein kinase.

Conclusions:

• Protein phosphorylation is likely involved in synaptic events at nicotinic cholinergic synapses.
• The acetylcholine receptor itself may be directly phosphorylated.
• Ionic conditions and cholinergic ligands modulate this phosphorylation process.