Expression of P2X2 and P2X3 receptor subunits in rat carotid body afferent neurones: role in chemosensory signalling.
1. Hypoxic chemotransmission in the rat carotid body (CB) is mediated in part by ATP acting on suramin-sensitive P2X purinoceptors. Here, we use RT-PCR, cloning and sequencing techniques to show P2X2 and P2X3 receptor expression in petrosal neurones, some of which develop functional chemosensory units with CB receptor clusters in co-culture. 2. Single-cell RT-PCR revealed that hypoxia-responsive neurones, identified electrophysiologically in co-culture, expressed both P2X2 and P2X3 mRNA. 3. Isohydric hypercapnia (10 % CO(2); pH 7.4) caused excitation of chemosensory units in co-culture. This excitation depended on chemical transmission, with ATP acting as a co-transmitter, since it was inhibited by reduction of the extracellular Ca(2+):Mg(2+) ratio and by the purinoceptor blocker suramin (50-100 microM). 4. Hypoxia and isohydric hypercapnia could separately excite the same chemosensory unit, and together the two stimuli interacted synergistically. 5. Using confocal immunofluorescence, co-localization of P2X2 and P2X3 protein was demonstrated in many petrosal somas and CB afferent terminals in situ. Taken together, these data indicate that ATP and P2X2-P2X3 purinoceptors play important roles in the peripheral control of respiration by carotid body chemoreceptors.
Prasad
M
M
Department of Biology, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1.
Fearon
I M
IM
Zhang
M
M
Laing
M
M
Vollmer
C
C
Nurse
C A
CA
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002245:Carbon Dioxide; D002344:Carotid Body / Q000166:cytology / Q000378:metabolism*; D002628:Chemoreceptor Cells / Q000502:physiology / Q000503:physiopathology; D005455:Fluorescent Antibody Technique; D006935:Hypercapnia / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology; D018613:Microscopy, Confocal; D009475:Neurons, Afferent / Q000378:metabolism*; D010313:Partial Pressure; D020033:Protein Isoforms / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000378:metabolism*; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D014018:Tissue Distribution
C546403:P2rx2 protein, rat; C546410:P2rx3 protein, rat; D020033:Protein Isoforms; D012333:RNA, Messenger; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; D002245:Carbon Dioxide; D000255:Adenosine Triphosphate