Limits...
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

The [Ca2+]i response to exogenous Ang IV in dissociated glomus cells of the rat carotid body from Nx control (A) and CH group (B). The records were made in cluster of 8-10 cells loaded with fura-2. Ang IV-induced [Ca2+]i elevation was more significant in the CH glomus cells than that of the Nx group. Note that the transient [Ca2+]i increase following the injection of Ang IV (0.01-10 μM) into the bath. In addition, histotoxic hypoxia with sodium cyanide (NaCN, 1 mM) increased the [Ca2+]i of the cells. Results are summarized in (C). On average, the [Ca2+]i elevation (ΔR (340/380)) induced by 10 μM Ang IV in the CH group (n=9) was significantly greater than that of the Nx control (n=7). Statistical significance (p<0.05, unpaired-t test) is shown in asterisk when comparing with the other groups.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2570565&req=5

Figure 4: The [Ca2+]i response to exogenous Ang IV in dissociated glomus cells of the rat carotid body from Nx control (A) and CH group (B). The records were made in cluster of 8-10 cells loaded with fura-2. Ang IV-induced [Ca2+]i elevation was more significant in the CH glomus cells than that of the Nx group. Note that the transient [Ca2+]i increase following the injection of Ang IV (0.01-10 μM) into the bath. In addition, histotoxic hypoxia with sodium cyanide (NaCN, 1 mM) increased the [Ca2+]i of the cells. Results are summarized in (C). On average, the [Ca2+]i elevation (ΔR (340/380)) induced by 10 μM Ang IV in the CH group (n=9) was significantly greater than that of the Nx control (n=7). Statistical significance (p<0.05, unpaired-t test) is shown in asterisk when comparing with the other groups.

Mentions: To investigate whether Ang IV stimulates intracellular Ca2+ response in the carotid body, the [Ca2+]i level was measured by spectrofluorimetry in fura-2-loaded glomus cells dissociated from the carotid bodies. Exogenous Ang IV (10 μM) elevated [Ca2+]i in clusters of glomus cells, although 0.1-1 μM Ang IV had only negligible effects on the [Ca2+]i levels (Fig. 4). The peak [Ca2+]i level was reached shortly following Ang IV stimulation and the [Ca2+]i levels gradually returned to the resting level within 3 minutes. In the CH glomus cells, the peak [Ca2+]i response to Ang IV was significantly greater that that of the Nx group (Fig. 4). On average, the levels of [Ca2+]i elevation induced by Ang IV (10 μM) were 51.0 ± 10.1 nM (n=9) and 13.4 ± 4.6 nM (n=7), respectively, in the CH and Nx group. Histotoxic hypoxia with sodium cyanide (1 mM) increased the [Ca2+]i level in all of the glomus cells. Results suggest that Ang IV can activate the [Ca2+]i response in the chemosensitive glomus cells and that the Ang IV-induced [Ca2+]i response is enhanced by CH.


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)

The [Ca2+]i response to exogenous Ang IV in dissociated glomus cells of the rat carotid body from Nx control (A) and CH group (B). The records were made in cluster of 8-10 cells loaded with fura-2. Ang IV-induced [Ca2+]i elevation was more significant in the CH glomus cells than that of the Nx group. Note that the transient [Ca2+]i increase following the injection of Ang IV (0.01-10 μM) into the bath. In addition, histotoxic hypoxia with sodium cyanide (NaCN, 1 mM) increased the [Ca2+]i of the cells. Results are summarized in (C). On average, the [Ca2+]i elevation (ΔR (340/380)) induced by 10 μM Ang IV in the CH group (n=9) was significantly greater than that of the Nx control (n=7). Statistical significance (p<0.05, unpaired-t test) is shown in asterisk when comparing with the other groups.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 4: The [Ca2+]i response to exogenous Ang IV in dissociated glomus cells of the rat carotid body from Nx control (A) and CH group (B). The records were made in cluster of 8-10 cells loaded with fura-2. Ang IV-induced [Ca2+]i elevation was more significant in the CH glomus cells than that of the Nx group. Note that the transient [Ca2+]i increase following the injection of Ang IV (0.01-10 μM) into the bath. In addition, histotoxic hypoxia with sodium cyanide (NaCN, 1 mM) increased the [Ca2+]i of the cells. Results are summarized in (C). On average, the [Ca2+]i elevation (ΔR (340/380)) induced by 10 μM Ang IV in the CH group (n=9) was significantly greater than that of the Nx control (n=7). Statistical significance (p<0.05, unpaired-t test) is shown in asterisk when comparing with the other groups.
Mentions: To investigate whether Ang IV stimulates intracellular Ca2+ response in the carotid body, the [Ca2+]i level was measured by spectrofluorimetry in fura-2-loaded glomus cells dissociated from the carotid bodies. Exogenous Ang IV (10 μM) elevated [Ca2+]i in clusters of glomus cells, although 0.1-1 μM Ang IV had only negligible effects on the [Ca2+]i levels (Fig. 4). The peak [Ca2+]i level was reached shortly following Ang IV stimulation and the [Ca2+]i levels gradually returned to the resting level within 3 minutes. In the CH glomus cells, the peak [Ca2+]i response to Ang IV was significantly greater that that of the Nx group (Fig. 4). On average, the levels of [Ca2+]i elevation induced by Ang IV (10 μM) were 51.0 ± 10.1 nM (n=9) and 13.4 ± 4.6 nM (n=7), respectively, in the CH and Nx group. Histotoxic hypoxia with sodium cyanide (1 mM) increased the [Ca2+]i level in all of the glomus cells. Results suggest that Ang IV can activate the [Ca2+]i response in the chemosensitive glomus cells and that the Ang IV-induced [Ca2+]i response is enhanced by CH.

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