Divergent roles of glycolysis and the mitochondrial electron transport chain in hypoxic pulmonary vasoconstriction of the rat: identity of the hypoxic sensor

1. The mechanisms responsible for sensing hypoxia and initiating hypoxic pu lmonary vasoconstriction (HPV) are unclear. We therefore examined the roles of the mitochondrial electron transport chain (ETC) and glycolysis in HPV of rat small intrapulmonary arteries (IPAs). 2. HPV demonstrated a transient constriction (phase 1) superimposed on a su stained constriction (phase 2). Inhibition of complex I of the ETC with rot enone (100 nM) or complex III with myxothiazol (100 nM) did not cause vasoc onstriction in normoxia, but abolished both phases of HPV. Rotenone inhibit ed the hypoxia-induced rise in intracellular Ca2+ ([Ca2+](i)). Succinate (5 nM), a substrate for complex II, reversed the effects of rotenone but not myxothiazol on HPV, but did not affect the rise in NAD(P)H fluorescence ind uced by hypoxia or rotenone. Inhibition of cytochrome oxidase with cyanide (100 muM) potentiated phase 2 constriction. 3. Phase 2 of HPV, but not phase 1, was highly correlated with glucose conc entration, being potentiated by 15 iyim but abolished in its absence, or fo llowing inhibition of glycolysis by iodoacetate or 2-deoxyglucose. Glucose concentration did not affect the rise in [Ca2+](i) during HPV. 4. Depolarisation-induced constriction was unaffected by hypoxia except in the absence of glucose, when it was depressed by similar to 50%. Depolarisa tion-induced constriction was depressed by rotenone during hypoxia bu 23 +/ - 4%; cyanide was without effect. 5. Hypoxia increased 2-deoxy-[H-3]glucose uptake in endothelium-denuded IPA s by 235 +/- 32%, and in mesenteric arteries by 218 +/- 38%. 6. We conclude that complex ITT of the mitochondrial ETC acts as the hypoxi c sensor in HPV, and initiates the rise in smooth muscle [Ca2+](i) by a mec hanism unrelated to changes in cytosolic redox state per se, but more proba bly by increased production of superoxide. Additionally, glucose and glycol ysis are essential for development of the sustained phase 2 of HPV, and sup port an endothelium-dependent Ca2+-sensitisation pathway rather than the ri se in [Ca2+](i).