Releasable pools and the kinetics of exocytosis in adrenal chromaffin cells.
Using high resolution capacitance (Cm) measurement techniques, we mapped the kinetics of exocytosis evoked by brief (5-100 ms) depolarizations that activate voltage-dependent Ca2+ channels in rat adrenal chromaffin cells. After correcting the Cm signal for contributions from Na+ channel-gating charge movements, the initial kinetics of exocytosis were consistent with depolarization-triggered release occurring initially from an immediately releasable pool of only approximately 17 secretory vesicles. In contrast, repetitive application of longer depolarizations evoked release from a distinct, larger readily releasable pool of approximately 170 vesicles. Our results suggest that the secretory response of a chromaffin cell to an action potential is limited by the size of the immediately releasable pool rather than by a fusion mechanism that is slower than that at synapses.
Horrigan
F T
FT
Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Florida 33101.
Bookman
R J
RJ
D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000502:physiology; D015550:Cell Degranulation / Q000502:physiology; D046508:Culture Techniques; D003992:Dibucaine / Q000494:pharmacology; D005089:Exocytosis; D007700:Kinetics; D008564:Membrane Potentials; D051381:Rats
D015220:Calcium Channels; D003992:Dibucaine; D002118:Calcium