title: Oxygen-sensitive reduction in Ca²⁺-activated K⁺ channel open probability in turtle cerebrocortex.
abstract: In response to low ambient oxygen levels the western painted turtle brain undergoes a large depression in metabolic rate which includes a decrease in neuronal action potential frequency. This involves the arrest of N-methyl-D-aspartate receptor (NMDAR) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) currents and paradoxically an increase in γ-aminobutyric acid receptor (GABAR) currents in turtle cortical neurons. In a search for other oxygen-sensitive channels we discovered a Ca(2+)-activated K(+) channel (K(Ca)) that exhibited a decrease in open time in response to anoxia. Single-channel recordings of K(Ca) activity were obtained in cell-attached and excised inside-out patch configurations from neurons in cortical brain sheets bathed in either normoxic or anoxic artificial cerebrospinal fluid (aCSF). The channel has a slope conductance of 223pS, is activated in response to membrane depolarization, and is controlled in a reversible manner by free [Ca(2+)] at the intracellular membrane surface. In the excised patch configuration anoxia had no effect on K(Ca) channel open probability (P(open)); however, in cell-attached mode, there was a reversible fivefold reduction in P(open) (from 0.5 ± 0.05 to 0.1 ± 0.03) in response to 30-min anoxia. The inclusion of the potent protein kinase C (PKC) inhibitor chelerythrine prevented the anoxia-mediated decrease in P(open) while drip application of a phorbol ester PKC activator decreased P(open) during normoxia (from normoxic 0.4 ± 0.05 to phorbol-12-myristate-13-acetate (PMA) 0.1 ± 0.02). Anoxia results in a slight depolarization of turtle pyramidal neurons (∼8 mV) and an increase in cytosolic [Ca(2+)]; therefore, K(Ca) arrest is likely important to prevent Ca(2+) activation during anoxia and to reduce the energetic cost of maintaining ion gradients. We conclude that turtle pyramidal cell Ca(2+)-activated K(+) channels are oxygen-sensitive channels regulated by cytosolic factors and are likely the reptilian analog of the mammalian large conductance Ca(2+)-activated K(+) channels (BK channels).
authors: Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5.
authors: C I
authors: CI
authors: Rodgers-Garlick
authors: D W
authors: DW
authors: Hogg
authors: L T
authors: LT
authors: Buck
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D001703:Biophysics; D002118:Calcium / Q000378:metabolism; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D000860:Hypoxia / Q000503:physiopathology; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism* / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010703:Phorbol Esters / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D011336:Probability; D017966:Pyramidal Cells / Q000187:drug effects; D026941:Sodium Channel Blockers / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014426:Turtles / Q000502:physiology*; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D018691:Excitatory Amino Acid Antagonists; D010703:Phorbol Esters; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D026941:Sodium Channel Blockers; C119222:phorbol-12-myristate; D013779:Tetrodotoxin; D019789:Tetraethylammonium; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; C056639:2-amino-5-phosphopentanoic acid; D014633:Valine; D010100:Oxygen; D002118:Calcium