Freezing eliminates a specific population of L-glutamate receptors in synaptic membranes

The binding of L-[3H]glutamate (L-Glu) to freeze-thawed synaptic membranes (SPMs) exhibited saturation kinetics, with Kd 507 nM and Bmax 6.99 pmol/mg protein. The effects of ions, the susceptibility to Triton X-100 and the pharmacological properties of the binding indicated that those sites detected in freeze-thawed SPMs were only of the Cl-/Ca2+-independent type. The Cl-/Ca2+-dependent (2-amino-4-phosphonobutyrate-sensitive) L-Glu binding sites which are additionally present in fresh SPMs are abolished by freezing.