Fast exocytosis and endocytosis triggered by depolarisation in single adrenal chromaffin cells before rapid Ca2+ current run-down.
The kinetics of exocytosis and membrane retrieval (endocytosis) were examined in bovine chromaffin cells using membrane capacitance measurement during whole-cell recording. At early times after breakthrough to the whole-cell recording mode, depolarisation for 1 s resulted in a fast (600 vesicles per s) exocytotic response and efficient membrane retrieval with a time constant of 25 s. The ability to activate fast exocytosis and retrieval was lost during intracellular dialysis, with a time constant of 40 s. At later times, a slow exocytotic response could be elicited with no membrane retrieval following single depolarisations. The wash-out of the responses appeared to be due to a rapid loss of a portion of the Ca2+ current. Trains of depolarisation at late times after breakthrough could elicit a fast (time constant 4 s) retrieval. These data show that in addition to a previously studied slow Ca(2+)-independent retrieval mechanism, chromaffin cells also possess an efficient and rapid retrieval pathway coupled to exocytosis that can be activated following depolarisation. The fast endocytosis appears to have a higher threshold for activation than exocytosis, probably due to a higher Ca2+ requirement. Rapid membrane retrieval appears to occur via a clathrin-independent pathway in chromaffin cells.
Burgoyne
R D
RD
Physiological Laboratory, University of Liverpool, UK.
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000200:Action Potentials; D000313:Adrenal Medulla / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002417:Cattle; D002838:Chromaffin System / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology; D003956:Dialysis; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D004705:Endocytosis; D005033:Ethylmaleimide / Q000494:pharmacology; D005089:Exocytosis; D008564:Membrane Potentials
D015220:Calcium Channels; D015124:8-Bromo Cyclic Adenosine Monophosphate; D004533:Egtazic Acid; D000242:Cyclic AMP; D005033:Ethylmaleimide; D002118:Calcium