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1 Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, Rhode Island 02912; 3 Department of Physiology and Biophysics, University of South Florida, Tampa, Florida 33612; and 2 Department of Medical Physiology, The University of Copenhagen, DK-2200 Copenhagen N, Denmark
Peptides with the Arg-Gly-Asp (RGD) motif
induce vasoconstriction in rat afferent arterioles by increasing the
intracellular Ca2+ concentration
([Ca2+]i) in vascular smooth muscle cells
(VSMC). This finding suggests that occupancy of integrins on the plasma
membrane of VSMC might affect vascular tone. The purpose of this study
was to determine whether occupancy of integrins by exogenous RGD
peptides initiates intracellular Ca2+ signaling in cultured
renal VSMC. When smooth muscle cells were exposed to 0.1 mM hexapeptide
GRGDSP, [Ca2+]i rapidly increased from
91 ± 4 to 287 ± 37 nM and then returned to the baseline
within 20 s (P < 0.05, 34 cells/5 coverslips). In
controls, the hexapeptide GRGESP did not trigger Ca2+
mobilization. Local application of the GRGDSP induced a regional increase of cytoplasmic [Ca2+]i, which
propagated as Ca2+ waves traveling across the cell and
induced a rapid elevation of nuclear [Ca2+]i.
Spontaneous recurrence of smaller-amplitude Ca2+ waves were
found in 20% of cells examined after the initial response to
RGD-containing peptides. Blocking dihydropyridine-sensitive Ca2+ channels with nifedipine or removal of extracellular
Ca2+ did not inhibit the RGD-induced Ca2+
mobilization. However, pretreatment of 20 µM ryanodine completely eliminated the RGD-induced Ca2+ mobilization.
Anti-
1 and anti-
3-integrin antibodies
with functional blocking capability simulate the effects of GRGDSP in
[Ca2+]i. Incubation with
anti-
1- or
3-integrin antibodies
inhibited the increase in [Ca2+]i induced by
GRGDSP. We conclude that exogenous RGD-containing peptides induce
release of Ca2+ from ryanodine-sensitive Ca2+
stores in renal VSMC via integrins, which can trigger cytoplasmic Ca2+ waves propagating throughout the cell.
confocal microscopy; immunofluorescence; calcium; wave
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