Hypoxic depression of PKG-mediated inhibition of serotonergic contraction in ovine carotid arteries

Abstract

Chronic hypoxia attenuates soluble guanylate cyclase-induced vasorelaxation in serotonin (5-HT)-contracted ovine carotid arteries. Because protein kinase G (PKG) mediates many effects of soluble guanylate cyclase activation through phosphorylation of multiple kinase targets in vascular smooth muscle, we tested the hypothesis that chronic hypoxia reduces the ability of PKG to phosphorylate its target proteins, which attenuates the ability of PKG to induce vasorelaxation. We also tested the hypothesis that hypoxia attenuates PKG expression and/or activity. Arteries from normoxic and chronically hypoxic (altitude of 3,820 m for 110 days) fetal and adult sheep were denuded of endothelium and equilibrated with 95% O2-5% CO2 in the presence of nitro-l-arginine methyl ester (l-NAME) and N(G)-nitro-l-arginine (l-NNA) to inhibit residual endothelial nitric oxide synthase. Concentration-response relations for 5-HT were determined in the presence of prazosin to minimize activation of α-adrenergic receptors. The PKG activator 8-(p-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (8-pCTP-cGMP) reduced agonist binding affinity of the 5-HT receptor in a concentration-dependent manner that was attenuated by hypoxia. Expression and activity of PKG-I was not significantly affected by chronic hypoxia in either fetal or adult arteries, although PKG-I abundance was greater in fetal arteries. Pretreatment with the large conductance calcium-sensitive potassium channel (BK) inhibitor iberiotoxin attenuated the vasorelaxation induced by 8-pCPT-cGMP in normoxic but not chronically hypoxic arteries. These results support the hypothesis that hypoxia attenuates the vasorelaxant effects of PKG through suppression of the ability of PKG to activate large conductance calcium-sensitive potassium channels in arterial smooth muscle. The results also reveal that this hypoxic effect is greater in fetal than adult arteries and that chronic maternal hypoxia can profoundly affect fetal vascular function.

Chronic Hypobaric Hypoxia Modulates Primary Cilia Differently in Adult and Fetal Ovine Kidneys

“…Both normoxic control and hypoxic animals were fed Alfalfa hay in a “keyhole” feeder in addition to providing a mineral block ad libitum . The animals were transported from Bishop to the laboratory immediately before the studies (Dasgupta et al, 2012 ; Thorpe et al, 2013 ).…”

Long-term hypoxia uncouples Ca2+and eNOS in bradykinin-mediated pulmonary arterial relaxation

“…The dichotomy between increased BK Ca channel ␣-subunit expression and diminished channel function is fascinating and can be the result of any one of a number of mechanisms. Potentially, LTH negatively affects channel function by diminishing the ability of protein kinase G to phosphorylate and activate channels (65), or the phosphorylation status of the protein could be modified in other ways (75). Additionally, there could be dysregulation of BK Ca ␣-/BK Ca ␤-colocalization akin to what we found in cerebral vessels (66).…”

Remodeling of Arterial Tone Regulation in Postnatal Development: Focus on Smooth Muscle Cell Potassium Channels

“…The effects of iberiotoxin on the contraction of sheep middle cerebral arteries also increased with age [ 40 ]. Later, this group also demonstrated an increase in the contractile responses of the carotid artery of adult sheep, but not fetuses, to 5-HT in the presence of iberiotoxin [ 78 ]. The effects of tetraethylammonium (TEA), another—albeit less selective—blocker of BK Ca channels, also intensified with age: TEA caused more pronounced contractions of the aortic segments of 8- and 12-week-old rats compared to newborns and 4-week-old animals [ 38 ].…”