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is associated with impaired calcium release in mesangial cells
1 Department of Medicine and 2 Department of Anatomy, Cell Biology, and Pathology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
Inositol
1,4,5-trisphosphate receptors (IP3Rs) mediate cytosolic
free calcium concentration
([Ca2+]c) signals in response to a
variety of agonists that stimulate mesangial cell contraction and
proliferation. In the present study, we demonstrate that
mesangial cells express both type I and III IP3Rs and that
these receptors occupy different cellular locations. Chronic treatment
with transforming growth factor-
1 (TGF-
1; 10 ng/ml, 24 h) leads
to downregulation of both type I and III IP3Rs as measured
by immunoblot and confocal analysis. TGF-
1 treatment does not affect
IP3 levels, and downregulation of type I IP3R
is not due to enhanced degradation of the protein, as the half-life of
type I IP3R is unchanged in the presence or absence of
TGF-
1. Functional effects of TGF-
1-induced downregulation of the
IP3Rs were evaluated by measuring
[Ca2+]c changes in response to
epidermal growth factor (EGF) in intact cells and sensitivity of
[Ca2+]c release to IP3
in permeabilized cells. TGF-
1 pretreatment led to a significant
decrease of [Ca2+]c release
induced by EGF in intact cells and by submaximal
IP3 (400 nm) in permeabilized cells. Total
IP3-sensitive [Ca2+]c
stores were not changed, as assessed by stimulation with maximal doses
of IP3 (10.5 µm) and thapsigargin-mediated calcium
release in permeabilized cells. We conclude that prolonged exposure to TGF-
1 leads to downregulation of both type I and III
IP3Rs in mesangial cells and this is associated with
impaired sensitivity to IP3.
transforming growth factor-
1; inositol 1,4,5-trisphosphate
receptors; calcium mobilization; mesangial cells
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