ATP-independent anoxic activation of ATP-sensitive K+ channels in dorsal vagal neurons of juvenile mice in situ.
The role of ATP in anoxic activation of ATP-sensitive K+ (KATP) channels was studied in dorsal vagal neurons of mouse brainstem slices. In the whole-cell configuration, cyanide-induced chemical anoxia evoked within 10 s a 300-pA outward current that gave rise to a hyperpolarization of 24 mV. These responses were mimicked by nitrogen-aerated saline, rotenone or diazoxide and abolished by tolbutamide. The cyanide-induced hyperpolarization was due to activation of 70 pS K(ATP) channels that were half-maximally blocked by 5 microM internal ATP. Dialyzing the cells with either 1, 20 or 0 mM ATP did not, however, affect the time to onset, the kinetics or the magnitude of the cyanide-induced hyperpolarization. Impairment of ATP consumption by ouabain, vanadate or reduced temperature had no effect either. Thus, anoxia-induced activation of these KATP channels cannot be explained by a fall of cellular ATP or a concomitant rise of ADP. Anoxia-related changes of the actin cytoskeleton or the composition of the plasma membrane are also not likely to be involved, as cytochalasin D did not affect the cyanide-evoked hyperpolarization and phosphatidylinositol 4,5-bisphosphate failed to decrease the ATP sensitivity of single KATP channels. Finally, because of a lack of effects of reduced/oxidized glutathione and the oxidase blocker diphenyliodonium on the cyanide-induced hyperpolarization, cellular redox state does not appear to be involved. Our results indicate that despite a high sensitivity to ATP in excised patches, anoxic activation of KATP channels is independent of cellular ATP. Rather the ATP block seems to be removed as a consequence of impaired mitochondrial function.
Müller
M
M
II. Physiologisches Institut, Georg-August-Universität Göttingen, Humboldtalle 23, D-37073 Göttingen, Germany.
Brockhaus
J
J
Ballanyi
K
K
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D003486:Cyanides / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology; D005978:Glutathione / Q000494:pharmacology; D002534:Hypoxia, Brain / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D008274:Magnesium / Q000494:pharmacology; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D051379:Mice; D008815:Mice, Inbred Strains; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D012402:Rotenone / Q000494:pharmacology; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D014044:Tolbutamide / Q000494:pharmacology; D014630:Vagus Nerve / Q000187:drug effects / Q000378:metabolism*
D003486:Cyanides; D015221:Potassium Channels; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters; D012402:Rotenone; D015638:Cytochalasin D; D000255:Adenosine Triphosphate; D014044:Tolbutamide; D000252:Calcium-Transporting ATPases; D005978:Glutathione; D008274:Magnesium