Brain Research 863 (2000) 143–150 www.elsevier.com / locate / bres Research report Calpain-mediated truncation of rat brain AMPA receptors increases their Triton X-100 solubility * Xiaoying Lu, Yongqi Rong, Ruifen Bi, Michel Baudry Neuroscience Program, University of Southern California, Hedco Neuroscience Bldg., Rm. 309, Los Angeles, CA 90089-2520, USA Accepted 1 February 2000 Abstract Previous studies have indicated that calpain activation results in the truncation of the C-terminal domains of AMPA and NMDA receptor subunits. The present study determined the distribution of the truncated species of the subunits between Triton-soluble and -insoluble fractions. Western blots were performed with various antibodies to quantify the amounts of the various species of GluR1, GluR2, GluR3 and NR2B subunits. The results indicate that calpain activation decreased the amount of all the intact subunits in Triton-insoluble fractions. Calpain-generated truncated forms of GluR1 and GluR2, but not NR2B, were absent in these fractions, and were recovered in Triton-soluble fractions. These findings suggest that calpain-mediated truncation of AMPA but not NMDA receptor C-terminal domains results in modifications of the interactions between the receptors and postsynaptic densities, and that this mechanism could be involved in activity-dependent changes in the subcellular distribution of AMPA receptors.  2000 Elsevier Science B.V. All rights reserved. Themes: Neurotransmitters, modulators, transporters, and receptors Topics: Excitatory amino acid receptors: physiology, pharmacology and modulation Keywords: Glutamate; Receptors; Calpain; Synapses; Plasticity 1. Introduction domains of AMPA and NMDA receptors regulates channel properties as well as interactions of the receptors with Glutamate ionotropic receptors play critical roles in targeting / anchoring proteins [5,18,27,32,33]. Little is synaptic transmission, synaptic plasticity and various known, however, regarding the processes involved in forms of neuropathology. The two major families of receptor turnover, and in particular, in receptor internaliza- glutamate ionotropic receptors, i.e. the AMPA and the tion and degradation. Reported values for AMPA receptor NMDA receptors, are now well characterized at the gene half-life are in the range of 30–50 h [2,15]. A complicating and structural levels. Significant progress has been made in factor in the case of AMPA receptors is the existence of a identifying proteins responsible for targeting and anchoring significant pool of non-synaptic receptors [3,4,21]. These the receptors in postsynaptic structures. Thus, several receptors are presumed to be present either in extra- families of proteins linking the C-terminal domains of synaptic membrane domains or in an intracellular vesicular various subunits of AMPA and NMDA receptors to compartment and could represent newly synthesized re- cytoskeletal proteins have been discovered [12,19,26,28]. ceptors targeted to synaptic regions [13,14,29]. Several posttranslational processes regulate the properties Another posttranslational modification for both AMPA of AMPA and NMDA receptors. Among these, phos- and NMDA receptors consists in the truncation of the phorylation processes have received considerable attention C-terminal domains of various subunits of both types of as phosphorylation / dephosphorylation of the C-terminal receptors [7–9]. This truncation is mediated by the cal- cium-dependent protease, calpain, and we showed it occurred under both physiological and pathological con- *Corresponding author. Tel.: 11-213-740-9188; fax: 11-213-740- ditions [6,8,9,25]. In the case of AMPA receptors, calpain- 5687. E-mail address: baudry@neuro.usc.edu (M. Baudry) mediated truncation of GluR1 subunits results in the 0006-8993 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0006-8993(00)02112-0