High CO2-bicarbonate buffer modifies GABAergic inhibitory effect at the crayfish neuromuscular synapse

Area of Science:

• Neuroscience
• Neurophysiology
• Comparative Physiology

Background:

• Gamma-aminobutyric acid (GABA) receptors are crucial for inhibitory neurotransmission.
• GABA-activated channels exhibit significant permeability to bicarbonate ions (HCO3-).
• The role of bicarbonate flux in modulating GABAergic inhibition remains incompletely understood.

Purpose of the Study:

• To investigate the impact of bicarbonate ion permeability on GABA-activated channel function.
• To determine how altered bicarbonate buffering affects synaptic inhibition efficacy.
• To analyze the consequences of bicarbonate shifts on postsynaptic potentials in a model system.

Main Methods:

• Electrophysiological recordings were performed on crayfish muscle preparations.
• Physiological solutions were saturated with a mixture of 15% CO2 and 85% O2 to alter bicarbonate buffering.
• Changes in inhibitory postsynaptic potential (IPSP) amplitude and reversal potential were measured.

Main Results:

• Increased CO2 significantly enhanced the depolarizing inhibitory postsynaptic potential (IPSP) amplitude by 290%.
• A shift of +8.33 mV in the IPSP reversal potential was observed under hypercapnic conditions.
• The inhibitory effect of IPSPs was reversed, leading to excitation of the excitatory postsynaptic potential.

Conclusions:

• GABA channel permeability to bicarbonate ions plays a critical role in synaptic inhibition.
• Altering bicarbonate buffering profoundly impacts neuronal excitability by modifying GABAergic signaling.
• These findings highlight the importance of physiological conditions in determining the functional outcome of GABAergic neurotransmission.