Superoxide generation links protein kinase C activation to impaired ATP-sensitive K+ channel function after brain injury.
BACKGROUND AND PURPOSE--Endothelin-1, in concentrations similar to that present in cerebrospinal fluid after fluid percussion brain injury (FPI), increases superoxide anion (O2-) production. Endothelin-1 also contributes to altered cerebral hemodynamics after FPI through impairment of ATP-sensitive K+ (KATP) channel function through protein kinase C (PKC) activation. Generation of O2- additionally occurs after FPI. Nitric oxide and cGMP elicit pial artery dilation through KATP channel activation. The present study was designed to determine whether PKC activation generates O2-, which, in turn, could link such activation to impaired KATP channel function after FPI. METHODS--Injury of moderate severity (1.9 to 2.1 atm) was produced by the lateral FPI technique in anesthetized newborn pigs equipped with a closed cranial window. Superoxide dismutase-inhibitable nitroblue tetrazolium (NBT) reduction was determined as an index of O2- generation. RESULTS--Phorbol 12, 13-dibutyrate (10(-6) mol/L), a PKC activator, increased superoxide dismutase-inhibitable NBT reduction from 1+/-1 to 37+/-5 pmol/mm2. Staurosporine (10(-7) mol/L), a PKC antagonist, blocked the NBT reduction after phorbol 12,13-dibutyrate and blunted the NBT reduction observed after FPI (1+/-1 to 15+/-2 versus 1+/-1 to 5+/-1 pmol/mm2 after FPI in the absence versus presence of staurosporine). Exposure of the cerebral cortex to a xanthine oxidase O2--generating system increased NBT reduction in a manner similar to FPI and blunted pial artery dilation to the KATP channel agonists cromakalim and calcitonin gene-related peptide, the nitric oxide releasers sodium nitroprusside and S-nitroso-N-acetylpenicillamine, and the cGMP analogue 8-bromo-cGMP (10+/-1% and 21+/-1% versus 4+/-1% and 9+/-1% for 10(-8) and 10(-6) mol/L cromakalim before and after activated oxygen-generating system exposure). CONCLUSIONS--These data show that PKC activation increases O2- production and contributes to such production observed after FPI. These data also show that an activated system that generates an amount of O2- similar to that observed with FPI blunted pial artery dilation to KATP channel agonists and nitric oxide/cGMP. These data suggest, therefore, that O2- generation links PKC activation to impaired KATP channel function after FPI.
Armstead
W M
WM
Departments of Anesthesia and Pharmacology, University of Pennsylvania and The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA. armteaw@mail.med.upenn.edu
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001160:Arterioles / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000098:blood supply / Q000201:enzymology; D001923:Brain Chemistry / Q000502:physiology; D001930:Brain Injuries / Q000378:metabolism*; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D002352:Carrier Proteins / Q000494:pharmacology; D002536:Cerebral Arteries / Q000187:drug effects / Q000201:enzymology; D019806:Cromakalim / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D008297:Male; D008565:Membrane Proteins / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism; D010841:Pia Mater / Q000098:blood supply; D015221:Potassium Channels / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism*; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013481:Superoxides / Q000378:metabolism*; D013552:Swine; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology; D033921:Vesicular Transport Proteins; D014969:Xanthine Oxidase / Q000378:metabolism
D002352:Carrier Proteins; D008565:Membrane Proteins; D015221:Potassium Channels; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D014665:Vasodilator Agents; D033921:Vesicular Transport Proteins; D019806:Cromakalim; D013481:Superoxides; D009599:Nitroprusside; C016276:8-bromocyclic GMP; D000255:Adenosine Triphosphate; D014969:Xanthine Oxidase; D011493:Protein Kinase C; D006152:Cyclic GMP; D015740:Calcitonin Gene-Related Peptide; D010100:Oxygen