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      Endothelium-derived NO, but not cyclic GMP, is required for hypoxic augmentation in isolated porcine coronary arteries.

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          Abstract

          The present study investigated the mechanism underlying the transient potentiation of vasoconstriction by hypoxia in isolated porcine coronary arteries. Isometric tension was measured in rings with or without endothelium. Hypoxia (Po(2) <30 mmHg) caused a transient further increase in tension (hypoxic augmentation) in contracted (with U46619) preparations. The hypoxic response was endothelium dependent and abolished by inhibitors of nitric oxide synthase [N(ω)-nitro-L-arginine methyl ester (L-NAME)] or soluble guanylyl cyclase (ODQ and NS2028). The addition of DETA NONOate (nitric oxide donor) in the presence of L-NAME restored the hypoxic augmentation, suggesting the involvement of the nitric oxide pathway. However, the same was not observed after incubation with 8-bromo-cyclic GMP, atrial natriuretic peptide, or isoproterenol. Assay of the cyclic GMP content showed no change upon exposure to hypoxia in preparations with and without endothelium. Incubation with protein kinase G and protein kinase A inhibitors did not inhibit the hypoxic augmentation. Thus the hypoxic augmentation is dependent on nitric oxide and soluble guanylyl cyclase but independent of cyclic GMP. The hypoxic augmentation persisted in calcium-free buffer and in the presence of nifedipine, ruling out a role for extracellular calcium influx. Hypoxia did not alter the intracellular calcium concentration, as measured by confocal fluorescence microscopy. This observation and the findings that hypoxic augmentation is enhanced by thapsigargin (sarco/endoplasmic reticulum calcium ATPase inhibitor) and inhibited by HA1077 or Y27632 (Rho kinase inhibitors) demonstrate the involvement of calcium sensitization in the phenomenon.

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          Author and article information

          Journal
          Am. J. Physiol. Heart Circ. Physiol.
          American journal of physiology. Heart and circulatory physiology
          1522-1539
          0363-6135
          Dec 2011
          : 301
          : 6
          Affiliations
          [1 ] Department of Pharmacology and Pharmacy, University of Hong Kong, Hong Kong.
          Article
          ajpheart.00258.2011
          10.1152/ajpheart.00258.2011
          21984543
          511ae80b-b33b-4973-b2fe-eefed413dfb2

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