PROTEIN-SYNTHESIS WITHIN DENDRITES - IONIC AND NEUROTRANSMITTER MODULATION OF SYNTHESIS OF PARTICULAR POLYPEPTIDES CHARACTERIZED BY GEL-ELECTROPHORESIS

This study evaluates whether physiological variables differentially af fect the local synthesis of protein constituents of synapses in subcel lular fractions containing pinched-off dendrites (synaptodendrosomes). Synaptodendrosomes were pulse-labeled in a medium containing S-35-met hionine with 3 or 25 mM KCl and in the presence or absence of 0.5 mM E GTA or 10 mu M glutamate. Synaptodendrosomes were then subfractionated to prepare synaptic plasma membranes and synaptic junctional complexe s. The protein constituents of the synaptic plasma membrane and synapt ic junctional complex fractions that were locally synthesized were ide ntified using SDS-PAGE and two-dimensional gel electrophoresis and the extent of labeling of individual bands was analyzed using a Phosphori mager. Analysis of incorporation into individual bands resolved by SDS -PAGE revealed that depolarizing conditions (25 mM KCI) increased the extent of labeling of different bands to a different extent (ranging f rom 10-70% increases in labeling). Addition of 0.5 mM EGTA decreased t he extent of labeling of the same group of bands in both 3 mM KCl and 25 mM KCl conditions. Addition of 10 mu M glutamate reduced incorporat ion especially in the synaptodendrosomes incubated in 25 mM KCl. Two-d imensional gel electrophoresis analyses revealed that the labeled spot s that showed differential labeling under the different conditions did not correspond to the most prominent Coomassie-stained spots. These r esults indicate that the proteins that are synthesized in synaptodendr osomes and regulated by physiological variables are not amongst the mo re abundant protein constituents of the fractions. Taken together, the se results are consistent with the idea that protein synthesis within dendrites may be regulated by synaptic activity.