[3H]dopamine depletion from osmotically defined storage sites: effects of reserpine, 53 mM KCl, and d-amphetamine.
A crude synaptosome-containing fraction (P2') prepared from rat striatal slices incubated with [3H]dopamine was exposed to hypoosmotic conditions and rapidly subjected to Millipore filtration. P2'-associated [3H]dopamine trapped on the filters was defined as hypoosmotic resistant, whereas P2'-associated [3H]dopamine that washed through the filters was defined as hypoosmotic sensitive. Electron microscopic examination of sections prepared from a P2' pellet that had been exposed to hypoosmotic conditions revealed extensive synaptosomal lysis. [3H]Dopamine accumulation and retention by the hypoosmotic-resistant fraction were reduced by reserpine. The proportional distribution of [3H]dopamine between hypoosmotic-resistant and -sensitive fractions was measured following in vitro exposure of the preloaded P2' fraction to reserpine, 53 mM KCl, and d-amphetamine. Each of these treatments resulted in a time-dependent loss of [3H]dopamine from the loaded P2' fraction without eliciting an alteration in the proportional distribution of [3H]dopamine between hypoosmotic-resistant and -sensitive fractions. Release induced by reserpine and d-amphetamine was independent of extrasynaptosomal Ca2+, whereas 53 mM KCl-induced release was dependent on extrasynaptosomal Ca2+. These results suggest that dopamine may be rapidly equilibrated between osmotically defined storage compartments, and thus specific compartmental depletion of loaded [3H]dopamine cannot be identified on the basis of osmotic lability.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003342:Corpus Striatum / Q000378:metabolism; D003913:Dextroamphetamine / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D008297:Male; D008854:Microscopy, Electron; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012110:Reserpine / Q000494:pharmacology*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure
D011189:Potassium Chloride; D012110:Reserpine; D002118:Calcium; D003913:Dextroamphetamine; D004298:Dopamine