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  • Title: Docked granules, the exocytic burst, and the need for ATP hydrolysis in endocrine cells.
    Author: Parsons TD, Coorssen JR, Horstmann H, Almers W.
    Journal: Neuron; 1995 Nov; 15(5):1085-96. PubMed ID: 7576652.
    Abstract:
    Ca(2+)-triggered exocytosis was studied in single rat melanotrophs and bovine chromaffin cells by capacitance measurements. Sustained exocytosis required MgATP, but even in the absence of MgATP, Ca2+ could trigger exocytosis of 2700 granules in a typical melanotroph and of 840 granules in a chromaffin cell. Granules undergoing ATP-independent exocytosis were similar in number to those appearing docked to the plasmalemma in quickly frozen unfixed sections (3300 in a melanotroph and 830 in a chromaffin cell). Most exocytosis required tens of seconds, but a small pool of granules was released in tens of milliseconds. Evidently, only a small subset of docked granules is rapidly releasable. We suggest that, temporally, the last ATP-dependent step in exocytosis is closely associated with docking and that docked granules reach fusion competence only after subsequent steps.
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