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

Background and Purpose-Pial artery dilation in response to activators of the ATP-sensitive Kt (KATP) 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 Kc, 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 KATP 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 NET reduction from 1 +/-1 to 23 +/-4 pmol/mm(2). Chelerythrine (10(-7) mol/L, a PKC inhibitor) blunted such NET reduction (1 +/-1 to 9 +/-2 pmol/mm(2)), whereas the vasopressin antagonist 1-(beta -mercapto-beta,beta -cyclopentamethylene propionic acid)2-(o-methyl) -Tyr-arginine vasopressin (MEAVP) blocked NET reduction. Chelerythrine and MEAVP also blunted the NET 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 Kt 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.