Gene expression and function of adenosine A(2A) receptor in the rat carotid body.
The present study was undertaken to determine whether rat carotid bodies express adenosine (Ado) A(2A) receptors and whether this receptor is involved in the cellular response to hypoxia. Our results demonstrate that rat carotid bodies express the A(2A) and A(2B) Ado receptor mRNAs but not the A(1) or A(3) receptor mRNAs as determined by reverse transcriptase-polymerase chain reaction. In situ hybridization confirmed the expression of the A(2A) receptor mRNA. Immunohistochemical studies further showed that the A(2A) receptor is expressed in the carotid body and that it is colocalized with tyrosine hydroxylase in type I cells. Whole cell voltage-clamp studies using isolated type I cells showed that Ado inhibited the voltage-dependent Ca(2+) currents and that this inhibition was abolished by the selective A(2A) receptor antagonist ZM-241385. Ca(2+) imaging studies using fura 2 revealed that exposure to severe hypoxia induced elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) in type I cells and that extracellularly applied Ado significantly attenuated the hypoxia-induced elevation of [Ca(2+)](i). Taken together, our findings indicate that A(2A) receptors are present in type I cells and that activation of A(2A) receptors modulates Ca(2+) accumulation during hypoxia. This mechanism may play a role in regulating intracellular Ca(2+) homeostasis and cellular excitability during hypoxia.
Kobayashi
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Department of Molecular and Cellular Physiology, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0576, USA.
Conforti
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Millhorn
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D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002344:Carotid Body / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D015687:Cell Hypoxia; D002478:Cells, Cultured; D005260:Female; D015870:Gene Expression; D017403:In Situ Hybridization; D007424:Intracellular Fluid / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D008297:Male; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1 / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D015220:Calcium Channels; D012333:RNA, Messenger; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1; D014446:Tyrosine 3-Monooxygenase; D002118:Calcium