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Drastic facilitation by α‐latrotoxin of bovine chromaffin cell exocytosis without measurable enhancement of Ca 2+ entry or [Ca 2+ ] i
Author(s) -
Michelena Pedro,
Fuente MaríaTeresa,
Vega Teresa,
Lara Baldomero,
López Manuela G.,
Gandía Luis,
García Antonio G.
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.481bj.x
Subject(s) - exocytosis , acetylcholine , chromaffin cell , chemistry , hepes , secretion , calcium , biophysics , stimulation , endocrinology , medicine , catecholamine , adrenal medulla , biochemistry , biology , organic chemistry
1 Latrotoxin (LTX, 1–3 n m ) caused a gradual increase of the supontaneous catecholamine release rate in bovine adrenal chromaffin cells superfused with normal Krebs–Hepes solution containing 2.5 m m Ca 2+ . Ca 2+ removal abolished this effect. LTX enhanced also the secretory responses to high K + (35 or 70 m m ) and to acetylcholine (ACh, 30 μ m ). 2 The application of Ca 2+ pulses to cells previously superfused with a 0 Ca 2+ solution (Krebs–Hepes deprived of CaCl 2 ) induced secretory responses that gradually reached 400–800 nA of catecholamines, provided that LTX was present. The responses to ACh or 35 m m K + pulses (in the presence of Ca 2+ ) were also enhanced by LTX, from around 100–200 nA to over 1000 nA. Though such enhancement remained in the presence of Ca 2+ channel blockers, it disappeared upon the lowering of [Na + ] 0 or in electroporated cells. 3 Using protocols similar to those of secretion, LTX did not enhance basal 45 Ca 2+ uptake, whole‐cell Ca 2+ currents or basal [Ca 2+ ]j. In fact, LTX attenuated the K + ‐ or ACh‐evoked increases in 45 Ca 2+ uptake and [Ca 2+ ] 1 . 4 It is proposed that the secretory response to brief periods of Ca 2+ reintroductions is triggered by local subplasmalemmal Ca 2+ 1 tranMents, produced by the Na + ‐Ca 2+ exchanger of the plasma membrane working in the reverse mode. This situation might be physiologically reproduced during ACh stimulation of chromaffin cells, which is followed by the firing of Na + ‐dependent action potentials.