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

Abstract

Chan CK, Mak J, Gao Y, Man RY, Vanhoutte PM. Endotheliumderived NO, but not cyclic GMP, is required for hypoxic augmentation in isolated porcine coronary arteries. Am J Physiol Heart Circ Physiol 301: H2313-H2321, 2011. First published October 7, 2011 doi:10.1152/ajpheart.00258.2011.-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 (PO2 Ͻ30 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 -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. soluble guanylyl cyclase; calcium sensitization; nitric oxide ENDOTHELIUM-DEPENDENT AUGMENTATION of contraction by hypoxia has been observed in canine femoral and coronary arteries (10,22,41), in the rat mesenteric artery (57), and in the human coronary artery (56). In the dog, augmented hypoxic coronary vasoconstrictions, which significantly reduce the blood supply to the cardiac muscle, occur in vivo only after previous ischemia-reperfusion injury (41). Considering that the hypoxic augmentation can be repeated consistently even after several episodes of exposure to hypoxia (10), this phenomenon could be important in patients (particularly if they have a previous history of coronary disease) exposed to repeated episodes of reduced oxygen content in the blood, as in the case for example in sleep apnea.The exact mechanism underlying hypoxic endothelium-dependent augmentation of vasoconstriction is not fully understood. Bioassay studies (45) on canine coronary arteries demonstrated that a diffusible substance released by the endothelium contributes to th...

cIMP synthesized by sGC as a mediator of hypoxic contraction of coronary arteries

“…Subsequent findings demonstrated that such a phenomenon, termed hypoxic augmentation of vasoconstriction (5, 15), occurs in a number of blood vessel types (5,7,8,15,21,23,25,26) contracted with norepinephrine (7, 8), phenylephrine (23), PGF 2␣ (15,25), and the TP receptor agonist U-46619 (21), indicating that it is not unique for a specific vasoconstrictor. It occurs in isolated coronary arteries with but not without endothelium (5,15,25,26). The phenomenon is not affected by bosentan, a blocker of endothelin receptors (5), but is prevented by inhibitors of nitric oxide (NO) synthase (5,15,25).…”

“…It occurs in isolated coronary arteries with but not without endothelium (5,15,25,26). The phenomenon is not affected by bosentan, a blocker of endothelin receptors (5), but is prevented by inhibitors of nitric oxide (NO) synthase (5,15,25). Hypoxic augmentation also occurs in arteries without endothelium treated with an exogenous NO donor (5) and is prevented by inhibitors of soluble guanylyl cyclase (sGC), including methylene blue, 1H-[1,2,4]oxadiazolo [4,3,-a]quinoxalin-1-one (ODQ), and NS-2028 (5,15).…”

PDE and sGC hand in hand to see the light

“…One cannot win both ways. We have, over the years, been confronted with other counterintuitive effects of sGC inhibitors, in that they prevent endothelium-dependent hypoxic vasoconstriction (7)(8)(9). We believe (9-11) that this can be explained by "biased" enzymatic activity of sGC, leading to the production of the noncanonical (12) vasoconstrictor cyclic nucleotide, inosine 3′,5′-cyclic monophosphate.…”

“…(1)] facilitate hypoxic vasoconstrictions (7), whereas PKG inhibitors do not affect them (8). Could it be that, like hypoxia, blue light by activating melanopsin initiates the production of noncanonical cyclic nucleotides by sGC?…”

11th International Symposium on Mechanisms of Vasodilation October 4-6, 2013, University Hospital Zurich, Switzerland

“…As shown by Gabor Rubanyi and Paul M. Vanhoutte [40], such contractions involve the transfer of an endothelium-derived mediator in the canine coronary artery. Paradoxically, the mediator in question appears to be nitric oxide, which activates soluble guanylyl cyclase [41]. The mechanism involved remained elusive until Yuasheng Gao reported at the symposium that hypoxia causes the latter enzyme to switch substrates and produce cyclic inosine monophosphate, which turns out to be a new second messenger causing coronary vaso constriction.…”