Vasopressin-induced protein kinase C-dependent superoxide generation contributes to atp-sensitive potassium channel but not calcium-sensitive potassium channel function impairment after brain injury.
OBJECTIVE
Pial artery dilation in response to activators of the ATP-sensitive K(+) (K(ATP)) and calcium-sensitive K(+) (K(Ca)) channels is impaired after fluid percussion brain injury (FPI). Vasopressin, when coadministered with the K(ATP) and K(Ca) channel agonists cromakalim and NS1619 in a concentration approximating that observed in cerebrospinal fluid (CSF) after FPI, blunted K(ATP) and K(Ca) channel-mediated vasodilation. Vasopressin also contributes to impaired K(ATP) and K(Ca) channel vasodilation after FPI. In addition, protein kinase C (PKC) activation generates superoxide anion (O(2)(-)), which in turn contributes to K(ATP) channel impairment after FPI. We tested whether vasopressin generates O(2)(-) in a protein kinase C (PKC)-dependent manner, which could link vasopressin release to impaired K(ATP) and K(Ca) channel-induced pial artery dilation after FPI.


METHODS
Injury of moderate severity (1.9 to 2.1 atm) was produced with 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 O(2)(-) generation.


RESULTS
Under sham injury conditions, topical vasopressin (40 pg/mL, the concentration present in CSF after FPI) increased superoxide dismutase-inhibitable NBT reduction from 1+/-1 to 23+/-4 pmol/mm(2). Chelerythrine (10(-7) mol/L, a PKC inhibitor) blunted such NBT reduction (1+/-1 to 9+/-2 pmol/mm(2)), whereas the vasopressin antagonist l-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid)2-(o-methyl)-Tyr-arginine vasopressin (MEAVP) blocked NBT reduction. Chelerythrine and MEAVP also blunted the NBT reduction observed after FPI (1+/-1 to 15+/-1, 1+/-1 to 4+/-1, and 1+/-1 to 5+/-1 pmol/mm(2) for sham-, chelerythrine-, and MEAVP-treated animals, respectively). Under sham injury conditions, vasopressin (40 pg/mL) coadministered with cromakalim or NS1619 blunted dilation in response to these K(+) channel agonists, whereas chelerythrine partially restored such impaired vasodilation for cromakalim but not NS1619. Cromakalim- and NS1619-induced pial artery dilation also was blunted after FPI. MEAVP partially protected dilation to both K(+) channel agonists after FPI, whereas chelerythrine did so for only cromakalim responses (for cromakalim at 10(-8) and 10(-6) mol/L, 13+/-1% and 23+/-1%, 2+/-1% and 5+/-1%, 9+/-1% and 15+/-2%, and 9+/-1% and 16+/-2% for sham-, FPI-, FPI-MEAVP-, and FPI-chelerythrine-pretreated animals, respectively).


CONCLUSIONS
These data show that vasopressin, in concentrations present in CSF after FPI, increased O(2)(-) production in a PKC-dependent manner and contributes to such production after FPI. These data show that vasopressin contributes to K(ATP) but not K(Ca) channel function impairment in a PKC-dependent manner after FPI and suggest that vasopressin contributes to K(Ca) channel function impairment after FPI via a mechanism independent of PKC activation.
Armstead
W M
WM
Departments of Anesthesia and Pharmacology, University of Pennsylvania, Philadelphia 19104, USA. armsteaw@mail.med.upenn.edu
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D001562:Benzimidazoles / Q000494:pharmacology; D001930:Brain Injuries / Q000150:complications / Q000378:metabolism*; D002545:Brain Ischemia / Q000209:etiology; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D019806:Cromakalim / Q000494:pharmacology; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000187:drug effects; D020536:Enzyme Activators / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008297:Male; D010841:Pia Mater / Q000098:blood supply; D015221:Potassium Channels / Q000819:agonists / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*; D013552:Swine; D014664:Vasodilation / Q000187:drug effects; D014667:Vasopressins / Q000378:metabolism* / Q000494:pharmacology; D014949:Wounds, Nonpenetrating; D014969:Xanthine Oxidase / Q000378:metabolism
D001562:Benzimidazoles; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D015221:Potassium Channels; D019806:Cromakalim; D014667:Vasopressins; D013481:Superoxides; C086491:NS 1619; D000255:Adenosine Triphosphate; D014969:Xanthine Oxidase; D011493:Protein Kinase C; D015740:Calcitonin Gene-Related Peptide