A kainate receptor is an ionotropic receptor activated by the neurotransmitter glutamate. Activation opens an ion channel, coupling chemical recognition to an electrical response. The family is named after kainic acid, an experimental agonist. Kainate receptors and AMPA receptors are distinct receptor families even though some experimental agonists can activate both, making pharmacological responses alone difficult to interpret.^[ref]

A genetic experiment helped isolate the kainate component. C. Mulle and colleagues generated mice lacking the subunit then called GluR6. Neurons in the hippocampal CA3 region became much less sensitive to kainic acid; a postsynaptic kainate current evoked by a train of mossy-fibre stimulation was absent in the mutants. This linked a molecular subunit to a synaptically evoked response, rather than merely to a response produced by bathing tissue in an agonist.^[ref] The subunit's current name is GluK2.^[ref]

For example, a current produced by an agonist that also activates AMPA receptors cannot be assigned wholly to kainate receptors. Comparing selective perturbations with synaptic stimulation supplies stronger evidence for the receptor responsible. In another experimental setting, paired recordings in ground-squirrel retina showed that AMPA receptors and kainate receptors could route cone signals into OFF retinal bipolar cells with different temporal filtering properties.^[ref]

Electron-ion recombination combines a free electron with a positive ion, reducing the number of free charge carriers. The released binding energy must be carried away, for example by a photon or another particle.

In an ionization chamber, recombination before charge collection reduces the measured signal. A simplified local model has loss rate $\alpha n_e{n}_i$, with coefficient $\alpha$ depending on the species and conditions. Increasing the collection field can reduce the time available for recombination, but complete collection must be established experimentally rather than assumed from the applied voltage alone.