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From the Center for Anesthesiology Research, Division of Anesthesiology and Critical Care Medicine, The Cleveland (Ohio) Clinic Foundation.
Correspondence to Paul A. Murray, PhD, Carl E. Wasmuth Chair and Director, Center for Anesthesiology Research-FF4, The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195. E-mail murrayp{at}cesmtp.ccf.org
Abstract Modulation of [Ca2+]i in
response to receptor activation is a critical determinant of vascular
smooth muscle tone. In this study, we examined the effect of continuous
stimulation of
1-adrenoceptors with
phenylephrine (PE) on [Ca2+]i in
single pulmonary artery smooth muscle cells (PASMCs) cultured
from explants of canine intrapulmonary artery. Fura 2loaded
PASMCs pretreated with propranolol (5 µmol/L) were
continuously superfused with PE at 37°C on the stage of an inverted
fluorescence microscope, and [Ca2+]i
was measured using a dual-wavelength spectrofluorometer. Resting values
of [Ca2+]i were 96±4 nmol/L. PE (10
µmol/L) stimulated oscillations in
[Ca2+]i at a frequency of 1.35±0.07/min,
which reached a peak [Ca2+]i of 650±26
nmol/L (n=69 cells). The oscillations lasted for >30
minutes and were constant in amplitude and frequency. Both the
amplitude and frequency of PE-induced [Ca2+]i
oscillations increased in a dose-dependent
(3x10-8 to 10-4
mol/L) manner. Pretreatment with the
1-adrenoceptor
antagonist prazosin (50 nmol/L) or removal of extracellular
Ca2+ abolished the repetitive
[Ca2+]i oscillations induced by
PE. The voltage-operated Ca2+ channel blockers
nifedipine (1 µmol/L) and verapamil
(1 µmol/L) had no effect on the
[Ca2+]i oscillations. In
contrast, inhibition of phospholipase C with U73122
(10-7 to 10-5 mol/L)
attenuated the oscillations in a dose-dependent fashion.
The nonselective protein kinase inhibitor
staurosporine (10-9 to
10-7 mol/L) had a minimal
inhibitory effect on the oscillations. Caffeine
(30 mmol/L) and thapsigargin (1 µmol/L) abolished the
oscillations, whereas pretreatment with ryanodine (1 to
100 µmol/L) had no effect. In freshly dispersed PASMCs, PE
(10 µmol/L) induced oscillations in
[Ca2+]i similar to those observed in cultured
cells, and patch-clamp experiments revealed oscillations in
membrane potential. These results indicate that PE induces
[Ca2+]i oscillations in PASMCs
via stimulation of
1-adrenoceptors coupled to
phospholipase C activation. Voltage-operated Ca2+ channels
and protein kinases are not required for the oscillations.
The requirement for extracellular Ca2+ and intracellular
Ca2+ stores indicates that both Ca2+ influx and
intracellular Ca2+ release play a role in the
maintenance of the oscillations.
Key Words: Ca2+ pulmonary artery
-adrenoceptor phospholipase C
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