The Journal of Neuroscience, July 1, 2000, 20(13):4776-4785
Bidirectional Modulation of Exocytosis by Angiotensin II Involves
Multiple G-Protein-Regulated Transduction Pathways in Chromaffin
Cells
Anja G.
Teschemacher and
Elizabeth
P.
Seward
Department of Pharmacology, School of Medical Sciences, University
of Bristol, Bristol BS3 1TD, United Kingdom
Angiotensin II (AngII) receptors couple to a multitude of different
types of G-proteins resulting in activation of numerous signaling
pathways. In this study we examined the consequences of this
promiscuous G-protein coupling on secretion. Chromaffin cells were
voltage-clamped at 
80 mV in perforated-patch configuration, and
Ca2+-dependent exocytosis was evoked with brief
voltage steps to +20 mV. Vesicle fusion was monitored by changes in
membrane capacitance (
Cm), and
released catecholamine was detected with single-cell amperometry.
Ca2+ signaling was studied by recording
voltage-dependent Ca2+ currents
(ICa) and by measuring intracellular
Ca2+
([Ca2+]i) with fura-2 AM.
AngII inhibited ICa (IC50 = 0.3 nM) in a voltage-dependent, pertussis toxin
(PTX)-sensitive manner consistent with Gi/o-protein coupling to Ca2+ channels.
Cm was modulated bi-directionally;
subnanomolar AngII inhibited depolarization-evoked exocytosis, whereas
higher concentrations, in spite of ICa
inhibition, potentiated Cm fivefold
(EC50 = 3.4 nM). Potentiation of
exocytosis by AngII involved activation of phospholipase C (PLC) and
Ca2+ mobilization from internal stores. PTX
treatment did not affect AngII-dependent Ca2+
mobilization or facilitation of exocytosis. However, protein kinase C
(PKC) inhibitors decreased the facilitatory effects but not the
inhibitory effects of AngII on stimulus-secretion coupling. The AngII
type 1 receptor (AT1R) antagonist losartan blocked both inhibition and
facilitation of secretion by AngII. The results of this study show that
activation of multiple types of G-proteins and transduction pathways by
a single neuromodulator acting through one receptor type can produce
concentration-dependent, bi-directional regulation of exocytosis.
Key words:
angiotensin II; G-protein-coupled receptor; calcium
channels; intracellular calcium stores; protein kinase C; phospholipase
C; pertussis toxin; exocytosis; chromaffin cells
Copyright © 2000 Society for Neuroscience 0270-6474/00/20134776-10$05.00/0
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