Kainate

Kainate receptors are a family of ionotropic glutamate receptors that are activated by kainic acid, a naturally occurring excitatory amino acid isolated from certain seaweeds. The receptor subunits, encoded by GRIK1–GRIK5 (also called GluK1–GluK5), assemble as tetrameric channels with distinct physiological properties depending on subunit composition. When opened by ligand binding, kainate receptors allow influx of Na+ and, in some subunit combinations, Ca2+, contributing to excitatory postsynaptic currents. They are located both postsynaptically, where they mediate fast excitation, and presynaptically, where they regulate the release of glutamate and other transmitters, thereby modulating synaptic transmission and network activity.

Kainate receptors are expressed throughout the central nervous system, with notable expression in the hippocampus, cortex, and amygdala. They participate in synaptic plasticity and network oscillations, and they can modulate neurotransmitter release in a frequency- and context-dependent manner. The exact roles of different GluK subunits vary, influencing receptor kinetics, Ca2+ permeability, and pharmacology.

The natural ligand kainic acid is a potent activator used in research and, at high doses, can induce seizures. Pharmacological tools include antagonists that block kainate receptors; some compounds preferentially target kainate over AMPA receptors, allowing selective study of kainate receptor function.

Excessive kainate receptor activation can contribute to excitotoxic neuronal injury and seizures, implicating them in epilepsy and brain injury. Altered kainate receptor signaling has also been investigated in neurodegenerative diseases and psychiatric conditions, though therapeutic strategies remain under development.

---