Neutral sphingomyelinase and protein kinase Cζ are involved in hypoxic pulmonary vasoconstriction

Abstract

Hypoxic pulmonary vasoconstriction (HPV) is a highly conserved physiological mechanism that optimizes blood oxygen saturation by increasing pulmonary vascular resistance in poorly aerated lung regions. We found that hypoxia increased ceramide content measured by immunocytochemistry, phosphorylation of the membrane NADPH oxidase subunit p47phox, reactive oxygen species production measured by either dihydroethidium or dichlorofluorescein fluorescence, inhibited voltage‐gated K+ (Kv) currents, depolarized the membrane and induced a vasoconstrictor response in isolated rat pulmonary arteries (PA). Inhibition of NAPDH oxidase, protein kinase Cζ (PKCζ), neutral sphingomyelinase (nSMase) abrogated the changes in reactive oxygen species, Kv currents and the vasoconstrictor response. nSMase inhibition also inhibited the increase in ceramide and prevented HPV in anesthetized open‐chest rats. The signaling pathway was specific for small PA as compared to mesenteric arteries. nSMase2 mRNA expression was ≈10 fold higher in small PA compared to large PA or mesenteric arteries. In conclusion, nSMase‐derived ceramide production and activation of PKCζ are early and necessary events in the signaling cascade of HPV leading to increased reactive oxygen species production, inhibition of Kv channels, depolarization and vasoconstriction. Supported by SAF2005‐03770, CIBER and Mutua Madrileñ