A comparative study of NETO1 and NETO2 on channel-opening kinetics of GluK2 kainate receptors

Neuropilin and tolloid-like proteins 1 and 2 (NETO1 and NETO2) are auxiliary subunits of kainate receptors, and GluK2 is a principal, pore-forming kainate receptor subunit. Kainate receptors are a subtype of ionotropic glutamate receptors. When coassembled with kainate receptors, NETO proteins are known to enhance the macroscopic current amplitude and affect channel properties such as channel desensitization rate. However, whether NETO proteins affect the rate of kainate receptor channel opening, which occurs in the microsecond time domain, is not known. Using a laser-pulse photolysis technique combined with whole-cell recording, we investigated the kinetic mechanism of channel opening of GluK2 homomeric receptors coexpressed with NETO1 and separately with NETO2 in human embryonic kidney-293 cells. We found that, as compared with GluK2 homomeric channels alone, NETO1 slows the channel-opening and channel-closing rate by ∼2-fold, whereas NETO2 slows these rates by ∼7-fold and ∼3-fold, respectively. Given that NETO2 also slows the rate of channel desensitization and reduces EC₅₀ value more significantly than NETO1, our results show that NETO2 seems to be the more impactful auxiliary subunit on GluK2 homomeric channels.