The Journal of Neurophysiology Vol. 84 No. 3 September 2000, pp. 1636-1644
Copyright ©2000 by the American Physiological Society

Augmentation of L-Type Calcium Current by Hypoxia in Rabbit Carotid Body Glomus Cells: Evidence for a PKC-Sensitive Pathway

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.