Alternative splicing of the NMDAR1 subunit affects modulation by calcium

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• The NMDA receptor (NMDAR) is crucial for synaptic plasticity and memory.
• Alternative splicing of the NR1 subunit generates variants with distinct functional properties.
• Understanding these variants is key to elucidating NMDAR roles in normal and disease states.

Purpose of the Study:

• To investigate the functional impact of Insert 1 and Insert 2 splice variants of the NR1 subunit on NMDAR-mediated currents.
• To characterize the calcium (Ca2+) dependency and ion flow properties of these splice variants.
• To determine the contribution of endogenous calcium-activated chloride currents (ICl(Ca)) to the observed slow inward current (Islow).

Main Methods:

• Expression of NR1 splice variants in Xenopus oocytes.
• Voltage-clamp electrophysiology to record NMDA-evoked currents.
• Manipulation of external Ca2+ concentrations and chloride levels.

Main Results:

• The presence of Insert 1 in NR1 subunits conferred a lower Ca2+ dependency for the slow inward current (Islow) at physiological Ca2+ levels.
• This reduced Ca2+ dependency was not due to altered divalent ion permeability or increased calcium entry.
• Islow is primarily mediated by current through the NMDAR ion channel, with a minor contribution from ICl(Ca).

Conclusions:

• The Insert 1 splice variant of the NR1 subunit modulates NMDAR Ca2+ dependency in a physiologically relevant manner.
• This modulation offers a potential mechanism for regulating glutamate transmission in both normal and pathological conditions.
• Alternative splicing of NR1 subunits provides a significant avenue for fine-tuning NMDAR function.