title: Membrane depolarization in PC-12 cells during hypoxia is regulated by an O2-sensitive K+ current.
abstract: The effects of hypoxia on K+ current (IK), resting membrane potential, and cytosolic free Ca2+ in rat pheochromocytoma (PC-12) cells were studied. Whole cell voltage- and current-clamp experiments were performed to measure IK and membrane potential, respectively. Cytosolic free Ca2+ level was measured using the Ca(2+)-sensitive fluorescent dye fura 2. Depolarizing voltage steps to +50 mV from a holding potential of -90 mV elicited a slowly inactivating, tetraethylammonium chloride-sensitive, and Ca(2+)-insensitive IK that was reversibly inhibited by reduced O2 tension. Graded reduction in PO2 (from 150 to 0 mmHg) induced a graded inhibition of O2-sensitive IK [IK(O2)] up to 46% at 0 mmHg. Moreover, hypoxia induced a 19-mV membrane depolarization and a twofold increase in cytosolic free Ca2+. In Ca(2+)-free condition, inhibition of IK(O2) induced an 8-mV depolarization, suggesting that inhibition of IK(O2) was responsible for initiating depolarization. The effect of reduced PO2 on the current-voltage relationship showed a reduction of outward current and a 14-mV shift in the reversal potential comparable with the amount of depolarization measured in current clamp experiments. Neither Ca(2+)-activated IK nor inwardly rectifying IK are responsible for the hypoxia-induced depolarization. In conclusion, PC-12 cells express an IK(O2), inhibition of which leads to membrane depolarization and increased intracellular Ca2+, making the PC-12 clonal cell line a useful model for studying the molecular and biophysical mechanisms that mediate O2 chemosensitivity.
authors.affiliation: Department of Molecular and Cellular Physiology, College of Medicine, University of Cincinnati, Ohio 45267-0576, USA.
authors.forename: W H
authors.initials: WH
authors.lastname: Zhu
authors.forename: L
authors.initials: L
authors.lastname: Conforti
authors.forename: M F
authors.initials: MF
authors.lastname: Czyzyk-Krzeska
authors.forename: D E
authors.initials: DE
authors.lastname: Millhorn
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D004594:Electrophysiology; D000860:Hypoxia / Q000503:physiopathology*; D008564:Membrane Potentials; D010100:Oxygen / Q000378:metabolism*; D016716:PC12 Cells / Q000502:physiology*; D010313:Partial Pressure; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000502:physiology*; D051381:Rats
chemical_list: D011188:Potassium; D010100:Oxygen; D002118:Calcium