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Carotid Body AT(4) Receptor Expression and its Upregulation in Chronic Hypoxia.

Fung ML, Lam SY, Wong TP, Tjong YW, Leung PS - Open Cardiovasc Med J (2007)

Bottom Line: Specific fluorescein-labeled Ang IV binding sites and positive staining of AT(4) immunoreactivity were mainly found in lobules in the carotid body.To examine if Ang IV induces intracellular Ca(2+) response in the carotid body, cytosolic calcium ([Ca(2+)](i)) was measured by spectrofluorimetry in fura-2-loaded glomus cells dissociated from CH and Nx carotid bodies.Exogenous Ang IV elevated [Ca(2+)](i) in the glomus cells and the Ang IV response was significantly greater in the CH than the Nx group.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Hong Kong, Pokfulam, Hong Kong.

ABSTRACT
Hypoxia regulates the local expression of angiotensin-generating system in the rat carotid body and the me-tabolite angiotensin IV (Ang IV) may be involved in the modulation of carotid body function. We tested the hypothesis that Ang IV-binding angiotensin AT(4) receptors play a role in the adaptive change of the carotid body in hypoxia. The expression and localization of Ang IV-binding sites and AT(4) receptors in the rat carotid bodies were studied with histochemistry. Specific fluorescein-labeled Ang IV binding sites and positive staining of AT(4) immunoreactivity were mainly found in lobules in the carotid body. Double-labeling study showed the AT(4) receptor was localized in glomus cells containing tyrosine hydroxylase, suggesting the expression in the chemosensitive cells. Intriguingly, the Ang IV-binding and AT(4) immunoreactivity were more intense in the carotid body of chronically hypoxic (CH) rats (breathing 10% oxygen for 4 weeks) than the normoxic (Nx) control. Also, the protein level of AT(4) receptor was doubled in the CH comparing with the Nx group, supporting an upregulation of the expression in hypoxia. To examine if Ang IV induces intracellular Ca(2+) response in the carotid body, cytosolic calcium ([Ca(2+)](i)) was measured by spectrofluorimetry in fura-2-loaded glomus cells dissociated from CH and Nx carotid bodies. Exogenous Ang IV elevated [Ca(2+)](i) in the glomus cells and the Ang IV response was significantly greater in the CH than the Nx group. Hence, hypoxia induces an upregulation of the expression of AT(4) receptors in the glomus cells of the carotid body with an increase in the Ang IV-induced [Ca(2+)]i elevation. This may be an additional pathway enhancing the Ang II action for the activation of chemoreflex in the hypoxic response during chronic hypoxia.

No MeSH data available.


Related in: MedlinePlus

Angiotensin IV (Ang IV)-binding sites in normoxic (Nx) and chronically hypoxic (CH) rat carotid body. Panels on top show FITC-coupled Ang IV binding (A), + Ang IV (B), + Sarile (C) in Nx group. Panels in middle show FITC-coupled Ang IV binding (D), + Ang IV (E), + Sarile (F) in CH group. Panels at bottom show FITC-coupled Ang IV binding (G), + Ang IV (H), + Sarile (I) in rat kidney, which was used as the positive control. Concentration of FITC-coupled Ang IV, unlabeled Ang IV and Sarile were 0.2, 10, 1 μM, respectively. Calibration bar is 20 μm.
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Figure 1: Angiotensin IV (Ang IV)-binding sites in normoxic (Nx) and chronically hypoxic (CH) rat carotid body. Panels on top show FITC-coupled Ang IV binding (A), + Ang IV (B), + Sarile (C) in Nx group. Panels in middle show FITC-coupled Ang IV binding (D), + Ang IV (E), + Sarile (F) in CH group. Panels at bottom show FITC-coupled Ang IV binding (G), + Ang IV (H), + Sarile (I) in rat kidney, which was used as the positive control. Concentration of FITC-coupled Ang IV, unlabeled Ang IV and Sarile were 0.2, 10, 1 μM, respectively. Calibration bar is 20 μm.

Mentions: Specific bindings of FITC-labeled Ang IV were obtained in the carotid body and also in the kidney served as a positive control. Fig. (1) shows the Ang IV-binding sites in the Nx (Fig. 1A) and CH (Fig. 1D) carotid body and in the kidney (Fig. 1G). The pattern of the labeling illustrates that the binding sites were localized in glomerular clusters in the carotid bodies, suggesting the expression in the chemosensitive glomus cells. In addition, the intensity of the fluorescence labeling was more intense in the CH than that of the Nx group. The binding was abolished by prior incubation of the sections with Ang IV without FITC labeling (Fig. 1B,E,H). Also, the FITC-labeled Ang IV binding was not affected by the addition of excessive amount of Sarile (Fig. 1C,F,I), which saturated the AT1 and AT2 binding sites.


Carotid Body AT(4) Receptor Expression and its Upregulation in Chronic Hypoxia.

Fung ML, Lam SY, Wong TP, Tjong YW, Leung PS - Open Cardiovasc Med J (2007)

Angiotensin IV (Ang IV)-binding sites in normoxic (Nx) and chronically hypoxic (CH) rat carotid body. Panels on top show FITC-coupled Ang IV binding (A), + Ang IV (B), + Sarile (C) in Nx group. Panels in middle show FITC-coupled Ang IV binding (D), + Ang IV (E), + Sarile (F) in CH group. Panels at bottom show FITC-coupled Ang IV binding (G), + Ang IV (H), + Sarile (I) in rat kidney, which was used as the positive control. Concentration of FITC-coupled Ang IV, unlabeled Ang IV and Sarile were 0.2, 10, 1 μM, respectively. Calibration bar is 20 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2570565&req=5

Figure 1: Angiotensin IV (Ang IV)-binding sites in normoxic (Nx) and chronically hypoxic (CH) rat carotid body. Panels on top show FITC-coupled Ang IV binding (A), + Ang IV (B), + Sarile (C) in Nx group. Panels in middle show FITC-coupled Ang IV binding (D), + Ang IV (E), + Sarile (F) in CH group. Panels at bottom show FITC-coupled Ang IV binding (G), + Ang IV (H), + Sarile (I) in rat kidney, which was used as the positive control. Concentration of FITC-coupled Ang IV, unlabeled Ang IV and Sarile were 0.2, 10, 1 μM, respectively. Calibration bar is 20 μm.
Mentions: Specific bindings of FITC-labeled Ang IV were obtained in the carotid body and also in the kidney served as a positive control. Fig. (1) shows the Ang IV-binding sites in the Nx (Fig. 1A) and CH (Fig. 1D) carotid body and in the kidney (Fig. 1G). The pattern of the labeling illustrates that the binding sites were localized in glomerular clusters in the carotid bodies, suggesting the expression in the chemosensitive glomus cells. In addition, the intensity of the fluorescence labeling was more intense in the CH than that of the Nx group. The binding was abolished by prior incubation of the sections with Ang IV without FITC labeling (Fig. 1B,E,H). Also, the FITC-labeled Ang IV binding was not affected by the addition of excessive amount of Sarile (Fig. 1C,F,I), which saturated the AT1 and AT2 binding sites.

Bottom Line: Specific fluorescein-labeled Ang IV binding sites and positive staining of AT(4) immunoreactivity were mainly found in lobules in the carotid body.To examine if Ang IV induces intracellular Ca(2+) response in the carotid body, cytosolic calcium ([Ca(2+)](i)) was measured by spectrofluorimetry in fura-2-loaded glomus cells dissociated from CH and Nx carotid bodies.Exogenous Ang IV elevated [Ca(2+)](i) in the glomus cells and the Ang IV response was significantly greater in the CH than the Nx group.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Hong Kong, Pokfulam, Hong Kong.

ABSTRACT
Hypoxia regulates the local expression of angiotensin-generating system in the rat carotid body and the me-tabolite angiotensin IV (Ang IV) may be involved in the modulation of carotid body function. We tested the hypothesis that Ang IV-binding angiotensin AT(4) receptors play a role in the adaptive change of the carotid body in hypoxia. The expression and localization of Ang IV-binding sites and AT(4) receptors in the rat carotid bodies were studied with histochemistry. Specific fluorescein-labeled Ang IV binding sites and positive staining of AT(4) immunoreactivity were mainly found in lobules in the carotid body. Double-labeling study showed the AT(4) receptor was localized in glomus cells containing tyrosine hydroxylase, suggesting the expression in the chemosensitive cells. Intriguingly, the Ang IV-binding and AT(4) immunoreactivity were more intense in the carotid body of chronically hypoxic (CH) rats (breathing 10% oxygen for 4 weeks) than the normoxic (Nx) control. Also, the protein level of AT(4) receptor was doubled in the CH comparing with the Nx group, supporting an upregulation of the expression in hypoxia. To examine if Ang IV induces intracellular Ca(2+) response in the carotid body, cytosolic calcium ([Ca(2+)](i)) was measured by spectrofluorimetry in fura-2-loaded glomus cells dissociated from CH and Nx carotid bodies. Exogenous Ang IV elevated [Ca(2+)](i) in the glomus cells and the Ang IV response was significantly greater in the CH than the Nx group. Hence, hypoxia induces an upregulation of the expression of AT(4) receptors in the glomus cells of the carotid body with an increase in the Ang IV-induced [Ca(2+)]i elevation. This may be an additional pathway enhancing the Ang II action for the activation of chemoreflex in the hypoxic response during chronic hypoxia.

No MeSH data available.


Related in: MedlinePlus