DEPLETION OF NEURONAL ENDOPLASMIC-RETICULUM CALCIUM STORES BY THAPSIGARGIN - EFFECT ON PROTEIN-SYNTHESIS

We have used thapsigargin (TG), a specific, irreversible inhibitor of endoplasmic reticulum (ER) Ca2+-ATPases, and caffeine, an agonist of t he ryanodine receptor, to study the effect of emptying of ER calcium s tores on protein synthesis in neuronal cells. TG at 1 mu M caused a pe rmanent inhibition of protein synthesis in hippocampal slices from 3-w eek-old rats but no inhibition in slices prepared from 2-month-old ani mals. Caffeine at 10 mM caused a reduction of protein synthesis in bot h 3-week- and 2-month-old rats immediately after exposure, but complet e recovery of protein synthesis occurred within 30 min after treatment . In neuronal cells, TG produced an almost complete inhibition of prot ein synthesis that was only partially reversed over a 24-h recovery pe riod. TG did not significantly affect neuronal ATP levels or energy ch arge. Fifty percent inhibition of protein synthesis was achieved with similar to 5 nM TG. Recovery of protein synthesis after TG treatment w as significantly hindered when serum was omitted from the medium after TG exposure, suggesting that serum promotes recovery of ER calcium ho meostasis. It is concluded that TG is a suitable tool for the study of the mechanisms of protein synthesis inhibition after transient cerebr al ischemia. The possibility that disturbances in ER calcium homeostas is may contribute to the pathological process of ischemic cell death i s discussed.