Phorbol ester translocation of protein kinase C in guinea-pig synaptosomes and the potentiation of calcium-dependent glutamate release.
The distribution of protein kinase C activity and specific phorbol ester binding sites between soluble and particulate fractions of isolated guinea-pig cerebral cortical synaptosomes is examined following preincubation with phorbol esters. Half-maximal decrease in cytosolic activity requires 10 nM 4 beta-phorbol myristoyl acetate. Specific [3H]phorbol dibutyrate binding sites are translocated from cytoplasmic to particulate fractions in parallel with protein kinase C activity. Depolarization of the plasma membrane by 30 mM KCl does not cause translocation of protein kinase C. 1 microM 4 beta-phorbol myristoyl acetate and 1 microM 4 beta-phorbol didecanoate (but not 1 microM 4 alpha-phorbol didecanoate) enhance the release of glutamate from synaptosomes partially depolarized by 10 mM KCl; however, 4 beta-phorbol myristoyl acetate is ineffective at 20 nM. 1 microM 4 beta-phorbol myristoyl acetate slightly increases the cytosolic free Ca2+ concentration of polarized synaptosomes, but not that following partial depolarization. 4 beta-Phorbol myristoyl acetate causes a concentration-dependent increase in the Ca2+-dependent glutamate release induced by sub-optimal ionomycin concentrations, but is without effect on the release induced by maximal ionomycin. It is concluded that phorbol esters stereospecifically enhance the Ca2+-sensitivity of glutamate release, but that higher concentrations may be required than for protein kinase C translocation in the same preparation. Instead the enhancement may be related to the rapid inactivation of protein kinase C which occurs with phorbol esters.
Díaz-Guerra
M J
MJ
Instituto de Bioquímica, Facultad de Farmacia, Madrid, Spain.
Sánchez-Prieto
J
J
Bosca
L
L
Pocock
J
J
Barrie
A
A
Nicholls
D
D
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D002118:Calcium / Q000502:physiology*; D002540:Cerebral Cortex / Q000201:enzymology / Q000378:metabolism; D004357:Drug Synergism; D005260:Female; D005971:Glutamates / Q000378:metabolism*; D006168:Guinea Pigs; D007473:Ion Channels / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D008297:Male; D010703:Phorbol Esters / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism
D005971:Glutamates; D007473:Ion Channels; D010703:Phorbol Esters; D011493:Protein Kinase C; D002118:Calcium