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(Received for publication, September 21, 1995; and in revised form, December 28, 1995) Parafollicular (PF) cells secrete 5-hydroxytryptamine in
response to increased extracellular Ca
Volume 271,
Number 11,
Issue of March 15, 1996 pp. 6441-6450
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
(
[Ca
]
).
This stimulus causes Cl
channels in PF secretory
vesicles to open, leading to vesicle acidification. PF cells express a
plasmalemmal heptahelical receptor (CaR) that binds
Ca
, Gd
, and Ba
.
We now report that the CaR mediates vesicle acidification.
Ca
, Gd
, and Ba
induced vesicle acidification, which was independent of
channel-mediated Ca
entry. Agonist-induced vesicle
acidification was blocked by pertussis toxin, inhibitors of
phosphatidylinositol-phospholipase C, calmodulin, NO synthase, guanylyl
cyclase, or protein kinase G. PF cells contained NO synthase
immunoreactivity, and vesicles were acidified by NO donors and
dibutyryl cGMP. [Ca
]
,
and Gd
mobilized thapsigargin-sensitive internal
Ca
stores. [
S]G
and [
S]G
were
immunoprecipitated from PF membranes incubated with agonists in the
presence of [
S]adenosine
5`-O-(thiotriphosphate). Labeling of G
but
not G
was antagonized by pertussis toxin. Vesicles
acidified in response to activation of protein kinase C; however,
protein kinase C inhibition blocked calcium channel- but not
CaR-dependent acidification. We propose the following signal
transduction pathway: CaR
G
phosphatidylinositol-phospholipase C
inositol
1,4,5-trisphosphate
[Ca
]
Ca
/calmodulin
NO synthase
NO
guanylyl cyclase
cGMP
protein kinase G
opens
vesicular Cl
channel.
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