Exocytosis elicited by action potentials and voltage-clamp calcium currents in individual pancreatic B-cells
Ämmälä, C. ; Eliasson, L. LU
; Bokvist, K
; Larsson, O.
; Ashcroft, F. M.
and Rorsman, P.
(1993)
In The Journal of Physiology
472.
p.665-688
- Abstract
- 1. Measurements of membrane capacitance, as an indicator of exocytosis, and intracellular Ca2+ concentration ([Ca2+]i) were used to determine the Ca2+ dependence of secretion in single pancreatic B-cells. 2. Exocytosis was dependent on a rise in [Ca2+]i and could be evoked by activation of voltage-dependent Ca2+ currents. The threshold for depolarization-induced release was 0.5 microM [Ca2+]i. Once the [Ca2+]i threshold was exceeded, exocytosis was rapidly (< 50 ms) initiated. When individual pulses were applied, exocytosis stopped immediately upon repolarization and the Ca2+ channels closed, although [Ca2+]i remained elevated for several seconds. 3. During repetitive stimulation (1 Hz), when [Ca2+]i attained micromolar levels,... (More)
- 1. Measurements of membrane capacitance, as an indicator of exocytosis, and intracellular Ca2+ concentration ([Ca2+]i) were used to determine the Ca2+ dependence of secretion in single pancreatic B-cells. 2. Exocytosis was dependent on a rise in [Ca2+]i and could be evoked by activation of voltage-dependent Ca2+ currents. The threshold for depolarization-induced release was 0.5 microM [Ca2+]i. Once the [Ca2+]i threshold was exceeded, exocytosis was rapidly (< 50 ms) initiated. When individual pulses were applied, exocytosis stopped immediately upon repolarization and the Ca2+ channels closed, although [Ca2+]i remained elevated for several seconds. 3. During repetitive stimulation (1 Hz), when [Ca2+]i attained micromolar levels, exocytosis also took place during the interpulse intervals albeit at a slower rate than during the depolarizations. 4. Exocytosis could be initiated by simulated action potentials. Whereas a single action potential only produced a small capacitance increase, and in some cells even failed to stimulate release, larger and more consistent responses were obtained with > or = four action potentials. 5. Comparison of the rates of exocytosis measured in response to depolarization, mobilization of Ca2+ from intracellular stores or infusion of Ca2+ through the patch pipette suggests that [Ca2+]i at the secretory sites attains a concentration of several micromolar. This is much higher than the average [Ca2+]i detected by microfluorimetry suggesting the existence of steep spatial gradients of [Ca2+]i within the B-cell. 6. Inclusion of inhibitors of Ca2+/calmodulin-dependent protein kinase II in the intracellular solution reduced the depolarization-induced exocytotic responses suggesting this enzyme may be involved in the coupling between elevation of [Ca2+]i to stimulation of the secretory machinery. 7. The size of the unitary exocytotic event was 2 fF, corresponding to a secretory granule diameter of 250 nm. 8. Over short periods, exocytosis may be extremely fast (1 pF/s or 500 granules/s), which is much higher than the rate of endocytosis (18 fF/s or 9 granules/s). Since the latter is in better agreement with the maximum rate of insulin secretion from islets (approximately 2 granules/s), we suggest that membrane retrieval may set an upper limit on the rate of exocytosis during extended periods of secretion. (Less)
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- author
- Ämmälä, C.
; Eliasson, L.
LU
; Bokvist, K
; Larsson, O.
; Ashcroft, F. M.
and Rorsman, P.
- publishing date
- 1993
- type
- Contribution to journal
- publication status
- published
- in
- The Journal of Physiology
- volume
- 472
- pages
- 665 - 688
- publisher
- The Physiological Society
- external identifiers
-
- scopus:0027763496
- ISSN
- 1469-7793
- DOI
- 10.1113/jphysiol.1993.sp019966
- language
- English
- LU publication?
- no
- id
- bf24a06f-1ebf-4c49-8ee3-6dac716c4876
- date added to LUP
- 2019-07-01 16:19:27
- date last changed
- 2023-07-10 04:04:58
@article{bf24a06f-1ebf-4c49-8ee3-6dac716c4876,
abstract = {{1. Measurements of membrane capacitance, as an indicator of exocytosis, and intracellular Ca2+ concentration ([Ca2+]i) were used to determine the Ca2+ dependence of secretion in single pancreatic B-cells. 2. Exocytosis was dependent on a rise in [Ca2+]i and could be evoked by activation of voltage-dependent Ca2+ currents. The threshold for depolarization-induced release was 0.5 microM [Ca2+]i. Once the [Ca2+]i threshold was exceeded, exocytosis was rapidly (< 50 ms) initiated. When individual pulses were applied, exocytosis stopped immediately upon repolarization and the Ca2+ channels closed, although [Ca2+]i remained elevated for several seconds. 3. During repetitive stimulation (1 Hz), when [Ca2+]i attained micromolar levels, exocytosis also took place during the interpulse intervals albeit at a slower rate than during the depolarizations. 4. Exocytosis could be initiated by simulated action potentials. Whereas a single action potential only produced a small capacitance increase, and in some cells even failed to stimulate release, larger and more consistent responses were obtained with > or = four action potentials. 5. Comparison of the rates of exocytosis measured in response to depolarization, mobilization of Ca2+ from intracellular stores or infusion of Ca2+ through the patch pipette suggests that [Ca2+]i at the secretory sites attains a concentration of several micromolar. This is much higher than the average [Ca2+]i detected by microfluorimetry suggesting the existence of steep spatial gradients of [Ca2+]i within the B-cell. 6. Inclusion of inhibitors of Ca2+/calmodulin-dependent protein kinase II in the intracellular solution reduced the depolarization-induced exocytotic responses suggesting this enzyme may be involved in the coupling between elevation of [Ca2+]i to stimulation of the secretory machinery. 7. The size of the unitary exocytotic event was 2 fF, corresponding to a secretory granule diameter of 250 nm. 8. Over short periods, exocytosis may be extremely fast (1 pF/s or 500 granules/s), which is much higher than the rate of endocytosis (18 fF/s or 9 granules/s). Since the latter is in better agreement with the maximum rate of insulin secretion from islets (approximately 2 granules/s), we suggest that membrane retrieval may set an upper limit on the rate of exocytosis during extended periods of secretion.}},
author = {{Ämmälä, C. and Eliasson, L. and Bokvist, K and Larsson, O. and Ashcroft, F. M. and Rorsman, P.}},
issn = {{1469-7793}},
language = {{eng}},
pages = {{665--688}},
publisher = {{The Physiological Society}},
series = {{The Journal of Physiology}},
title = {{Exocytosis elicited by action potentials and voltage-clamp calcium currents in individual pancreatic B-cells}},
url = {{http://dx.doi.org/10.1113/jphysiol.1993.sp019966}},
doi = {{10.1113/jphysiol.1993.sp019966}},
volume = {{472}},
year = {{1993}},
}