Effects of phosphorylation and cytoskeleton-affecting reagents on GABA(A) receptor recruitment into synaptosomes following acute stress.

The [3H]-flunitrazepam receptor density, measured ex vivo in synaptosomes at 4 degrees C, increased by about 30% because of acute stress in chicks. This increase was first reported to be a receptor recruitment due to the fact that the increase induced by subsolubilizing concentrations of Triton X-100 was not additive to the receptor increase induced by acute stress [J Neural Transm 87 (1992) 97]. In synaptosomal membranes from stressed chicks, the incorporation of alkaline phosphatase or ATP into the lumen abolished or increased, respectively, the receptor unmasking after incubation at 4 and 37 degrees C, suggesting that phosphorylation plays a role in the recruitment mechanism. Moreover, both colchicine and vinblastine, but not taxol, abolished the recruitment induced by stress at 37 degrees C only in synaptosomes, suggesting that micrutubule depolymerization plays a role in the masking of receptors. Furthermore, both cytochalasins C and D induced an increase of the receptor density, abolished by N-ethylmaleimide, in both the stressed and nonstressed conditions, suggesting that microfilament depolymerization induced the exposure to the radioligand of a cytosolic vesicular receptor pool, which had not fused yet with the postsynaptic membrane.