Mg2blockaden

Mg2blockaden, or magnesium blockades, describe the blocking action of magnesium ions (Mg2+) on certain ion channels, most prominently the NMDA receptor channel, which regulates ion flow across the postsynaptic membrane.

In NMDA receptors, Mg2+ enters the channel pore and blocks the flow of Na+ and Ca2+ at resting membrane potential. The block is voltage-dependent: depolarization reduces the affinity of Mg2+ for the pore and ejects the ion, allowing ion conduction when the receptor is activated by glutamate (and a co-agonist such as glycine).

The relief of Mg2+ block is essential for the receptor’s role as a coincidence detector in synaptic transmission. Only when presynaptic input releases glutamate and the postsynaptic neuron is sufficiently depolarized does Ca2+ influx occur through NMDA receptors, triggering intracellular signaling pathways that contribute to synaptic plasticity, learning and memory.

Physiological and experimental relevance: Mg2+ block helps set the threshold for NMDA receptor activation under normal conditions and influences neuronal excitability. In research, altering extracellular Mg2+ concentration or applying specific antagonists aids in characterizing NMDA receptor properties and function. While NMDA receptors are the primary context for Mg2+ block, magnesium interactions with other channels exist but are less central to this mechanism.