Oxygen sensors in vascular smooth muscle.
Inhibition or activation of cellular function due to acute decreases in PO2 can be considered in terms of two different processes: 1) a sensor that monitors PO2 decreases and 2) transduction systems directed from the O2 sensor to reactions that control cellular function. We used the norepinephrine-contracted aortic smooth muscle model to study the nature of the O2 sensor and transduction system during decreased PO2-evoked relaxations. The phosphorylation potential, a measurement of kinetic energy required for ATP hydrolysis, was decreased to 30% of control at the onset of relaxation and progressively fell as muscle relaxed. The free inorganic phosphate intracellular concentration ([Pi]) was experimentally increased approximately 0.6 mM during transients that followed a rapid decrease in PO2. Relaxations to 80% of maximal force were more rapid under conditions of an augmented [Pi] than in control rings, and they occurred at a higher phosphocreatine concentration and phosphocreatine-to-free creatine ratio but at the same phosphorylation potential. Results support the operation of a cytochrome aa3 O2 sensor in the mechanism of decreased PO2-evoked relaxations and implicate an increase in [Pi] and a decrease in kinetic energy in the transduction mechanism directed at rate-limiting reactions that control force.
Katayama
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Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia 19104.
Coburn
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Fillers
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Baron
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001011:Aorta; D003401:Creatine / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D013053:Spectrophotometry
D010710:Phosphates; D010725:Phosphocreatine; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D003576:Electron Transport Complex IV; D003401:Creatine; D010100:Oxygen; D009638:Norepinephrine