Different secretory vesicles can be involved in depolarization-evoked exocytosis.
The relationship between Ca(2+) influx through voltage-activated Ca(2+) channels, resting intracellular Ca(2+) level (Ca(i)) and Ca(2+)-dependent exocytosis was studied in bovine adrenal chromaffin cells by using patch-clamp, capacitance, and fluorescent measurements. It was established that depolarization-induced exocytosis passed over two steps, both of which linearly depend on Ca(i). At Ca(i) lying below critical point (200-300 nM) the slope of the relationship was 4.43 and at Ca(i) exceeding the critical point the slope was equal to 31.63. The vesicular mechanism describing experimental two-step dependence of exocytosis on intracellular Ca(2+) (Ca(i)) is proposed. According to the model at Ca(i) below critical point only small-sized vesicles fuse with plasma membrane, whereas at higher Ca(i), larger vesicles started to fuse.
Lukyanetz
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EA
Bogomoletz Institute of Physiology, Bogomoletz Str. 4, Kiev-24, 01024, Ukraine. elena@serv.biph.kiev.ua
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002417:Cattle; D002460:Cell Line; D019439:Chromaffin Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D025802:Electric Capacitance; D005089:Exocytosis / Q000187:drug effects; D005453:Fluorescence; D016257:Fura-2 / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*
D011493:Protein Kinase C; D002118:Calcium; D016257:Fura-2