title: Loading of oxidizable transmitters into secretory vesicles permits carbon-fiber amperometry.
abstract: Carbon-fiber amperometry detects oxidizable molecules released by exocytosis. We extended this electrochemical technique to cells that do not normally secrete oxidizable transmitters. We incubated AtT-20 cells, pituitary gonadotropes, cultured cerebellar granule cells, and yeast with high concentrations of dopamine (DA) and observed spontaneous and evoked quantal release of DA by amperometry. The rate of detectable spontaneous amperometric events was used as a measure of loading in AtT-20 cells. With 70 mm DA in the bath, loading was complete within 40 min. Cytoplasmic accumulation preceded vesicular loading. Loading decreased proportionally as the bath DA concentration was lowered. Loading rates were similar at 37 and 25 degrees C and much slower at 15 degrees C. Loading was blocked by bafilomycin A(1), a proton pump inhibitor, but not by bupropion, an inhibitor of the plasma membrane DA transporter. Other cells were tested. Spontaneous quantal events became more frequent and evoked events became larger and more frequent when PC12 cells were loaded with DA. Fluid-phase loading of neurons by short stimulation in DA solutions seemed selective for the synaptic vesicles. Thus, many cell types can be loaded with DA to study spontaneous and evoked exocytosis. The amine molecules enter these cells passively and may become concentrated in acidic vesicles by protonation.
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195-7290, USA.
authors.forename: K T
authors.initials: KT
authors.lastname: Kim
authors.forename: D S
authors.initials: DS
authors.lastname: Koh
authors.forename: B
authors.initials: B
authors.lastname: Hille
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism / Q000494:pharmacology; D050483:Dopamine Plasma Membrane Transport Proteins; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry / Q000295:instrumentation / Q000379:methods*; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D051379:Mice; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents / Q000378:metabolism* / Q000494:pharmacology; D010084:Oxidation-Reduction / Q000187:drug effects; D016716:PC12 Cells; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D054328:Proton Pump Inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*; D013696:Temperature
chemical_list: D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D054328:Proton Pump Inhibitors; D004298:Dopamine