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The Journal of Neurophysiology Vol. 84 No. 3 September 2000, pp. 1636-1644
Copyright ©2000 by the American Physiological Society
Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
Summers, Beth A.,
Jeffrey L. Overholt, and
Nanduri R. Prabhakar.
Augmentation of L-Type Calcium Current by Hypoxia in Rabbit
Carotid Body Glomus Cells: Evidence for a PKC-Sensitive Pathway. J. Neurophysiol. 84: 1636-1644, 2000. Previous studies have suggested that voltage-gated
Ca2+ influx in glomus cells plays a critical role
in sensory transduction at the carotid body chemoreceptors. The purpose
of the present study was to determine the effects of hypoxia on the
Ca2+ current in glomus cells and to elucidate the
underlying mechanism(s). Experiments were performed on freshly
dissociated glomus cells from rabbit carotid bodies.
Ca2+ current was monitored using the whole cell
configuration of the patch-clamp technique, with
Ba2+ as the charge carrier. Hypoxia
(pO2 = 40 mmHg) augmented the Ca2+ current by 24 ± 3% (n = 42, at 0 mV) in a voltage-independent manner. This effect was seen in
a CO2/HCO3
-, but not
in a HEPES-buffered extracellular solution at pH 7.4 (n = 6). When the pH of a HEPES-buffered extracellular solution was
lowered from 7.4 to 7.0, hypoxia augmented the
Ca2+ current by 20 ± 5% (n = 4, at 0 mV). Nisoldipine, an L-type Ca2+
channel blocker (2 µM, n = 6), prevented, whereas,
-conotoxin MVIIC (2 µM, n = 6), an inhibitor of N
and P/Q type Ca2+ channels, did not prevent
augmentation of the Ca2+ current by hypoxia,
implying that low oxygen affects L-type Ca2+
channels in glomus cells. Protein kinase C (PKC) inhibitors, staurosporine (100 nM, n = 6) and bisindolylmaleimide
(2 µM, n = 8, at 0 mV), prevented, whereas, a protein
kinase A inhibitor (4 nM PKAi, n = 10) did not prevent
the hypoxia-induced increase of the Ca2+ current.
Phorbol 12-myristate 13-acetate (PMA, 100 nM), a PKC activator,
augmented the Ca2+ current by 20 ± 3%
(n = 8, at 0 mV). In glomus cells treated with PMA
overnight (100 nM), hypoxia did not augment the
Ca2+ current (
3 + 4%, n = 5, at 0 mV). Immunocytochemical analysis revealed PKC
-like
immunoreactivity in the cytosol of the glomus cells. Following hypoxia
(6% O2 for 5 min), PKC-like immunoreactivity translocated to the plasma membrane in 87 ± 3% of the cells,
indicating PKC activation. These results demonstrate that hypoxia
augments Ca2+ current through L-type
Ca2+ channels via a PKC-sensitive mechanism.
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