Functional diversity of recombinant human AMPA type glutamate receptors: possible implications for selective vulnerability of motor neurons
Lower motor neurons are known to be susceptible to glutamate-mediated cell damage via overstimulation of AMPA type glutamate receptors (GluR). The molecular basis of an important hypothesis in investigating amyotrophic lateral sclerosis (ALS) is glutamate-excitotoxicity. The aim of this study was to define desensitization and deactivation kinetics of recombinant human GluR1 and GluR2 receptor channels and their splice variants by means of patch-clamp experiments employing ultrafast solution exchange techniques. By this approach, the desensitization time constants of homooligomeric channels could be measured as tau(Des)=2.95+/-0.22 ms (n=10) for GluR1flip, tau(Des)=3.17+/-0.19 ms (n=10) for GluR1flop, tau(Des)=9.86+/-0.79 ms (n=10) for GluR2flip, and tau(Des)=1.87+/-0.26 ms (n=10) for GluR2flop, respectively. In the case of GluR1flip/flop and GluR2flop, a nondesensitising steady state current of less than 1% of peak current amplitude was observed, while GluR2flip channel currents showed a marked steady state component of about 10% of the maximum current. No significant differences were detected comparing the deactivation time course of GluR1 and GluR2 splice variants. These results suggest that the human GluR subtypes tested comprise no fundamental difference to their rodent analogous. Therefore, we describe a preparation that will be useful for further investigation of motor neuron physiological properties and a methodological approach allowing to study functional recombinant human GluR channels under reliable conditions.