doi:10.1369/jhc.5A6755.2005
Volume 54 (4): 467-472, 2006 Copyright ©The Histochemical Society, Inc. Expression of Tandem P Domain K+ Channel, TREK-1, in the Rat Carotid Body
Laboratory of Veterinary Anatomy, Faculty of Agriculture, Iwate University, Morioka, Japan Correspondence to: Y. Yamamoto, Laboratory of Veterinary Anatomy, Department of Veterinary Sciences, Faculty of Agriculture, Iwate University, Ueda 3-19-8, Morioka, Iwate 080-8550, Japan. E-mail: yyoshio{at}iwate-u.ac.jp
TREK-1 is one of the important potassium channels for regulating membrane excitability. To examine the distribution of TREK-1 in the rat carotid body, we performed RT-PCR for mRNA expression and in situ hybridization and immunohistochemistry for tissue distribution of TREK-1. RT-PCR detected mRNA expression of TREK-1 in the carotid body. Furthermore, in situ hybridization revealed the localization of TREK-1 mRNA in the glomus cells. TREK-1 immunoreactivity was mainly distributed in the glomus cells and nerve fibers in the carotid body. TREK-1 may modulate potassium current of glomus cells and/or afferent nerve endings in the rat carotid body. (J Histochem Cytochem 54:467472, 2006)
Key Words: 2P-domain potassium channel carotid body membrane potential immunocytochemistry rat
TANDEM P DOMAIN K+ (K2P) channels can be divided into several subfamilies (see review; Lesage 2003
Several potassium channels show an oxygen-sensing property: TASK-1 in cerebellar granule neurons (Plant et al. 2002 To examine the distribution of TREK-1 in the rat carotid body, we performed RT-PCR for mRNA expression and in situ hybridization and immunohistochemistry for tissue distribution of TREK-1. Furthermore, double immunofluorescence by use of several cell markers was performed to identify cellular distribution of TREK-1.
Animals Wistar rats of both sexes (n=10) were used in our studies, which were approved by the local Ethics Committee. For RT-PCR analysis, four rats were sacrificed in the chamber filled with diethyl ether gas, and the bifurcations of carotid arteries were corrected. Whole carotid body was further dissected out with dissecting microscope and moved into RNA stabilization reagent (RNAlater; Qiagen, Tokyo, Japan). For immunohistochemistry and in situ hybridization, six rats were anesthetized intraperitoneally with pentobarbital (15 mg/kg) and transcardially perfused with Ringer's solution (500 ml) followed by Zamboni's fixative (4% paraformaldehyde, 0.5% picric acid in 0.1 M phosphate buffer; pH 7.4, 500 ml). The bifurcations of carotid arteries were dissected out and further fixed in the same fixative for 5 hr. The tissues were then soaked in 30% sucrose in phosphate-buffered saline (PBS; pH 7.4) and frozen. They were serially sectioned at 8 µm and mounted on glass slides coated with chrome alumgelatin.
RT-PCR Amplification
In Situ Hybridization For in situ hybridization, sections were washed with PBS and then rinsed with 5x SSC. The sections were incubated with 50% formamide in 5x SSC including 1 µg/ml digoxygenin-labeled oligonucleotide probe for TREK-1 (accession number AF385402; position 12641308; 5'-CACCGACAGGGTCCTCCTACATGGAGTCAGTTCCTGGTTATGGTT-3') with 40 µg/ml fragmented salmon sperm DNA for 15 hr at 50C. Sections were then washed in 5x SSC, 2x SSC, 0.1x SSC, and buffer 1 (constitute; 100 mM Tris, 150 mM NaCl, pH 7.5) and incubated with 1% normal goat serum in buffer 1 for 1 hr at room temperature. Sections were then washed with buffer 1 and reacted with alkaline phosphatase-labeled sheep anti-digoxygenin antibody Fab fragment (1:2000; Roche Diagnostics, Mannheim, Germany) for 2 hr at 40C. Sections were washed with buffer 1 and buffer 3 (100 mM Tris, 150 mM NaCl, 50 mM MgCl2, pH 9.5) and incubated with 5-bromo-4-chloro-3-indolyl phosphate/nitroblue tetrazolium solution for visualization of reacted sites. For positive control, antisense dioxygenin-labeled oligonucleotide probe for poly-A was used. For negative control, randomized digoxygenin-labeled oligonucleotide probes were used.
Immunohistochemistry
Double Immunofluorescence Cryostat sections were also used for double immunofluorescence for TREK-1 with synaptophysin, glial fibrillary acidic protein (GFAP), vimentin, or -smooth muscle actin (ASMA). After incubation with normal donkey serum, sections were incubated with goat polyclonal TREK-1 together with antibody against mouse monoclonal antibody against synaptophysin, rabbit polyclonal antibody against GFAP, mouse monoclonal antibody against vimentin, or mouse monoclonal antibody against ASMA for 12 hr at 4C. Sections were then incubated with a mixture of TRITC-labeled donkey anti-goat IgG with FITC-labeled donkey anti-mouse IgG or with FITC-labeled donkey anti-rabbit IgG for 2 hr at 25C. Sections were coverslipped with glycerol-PBS and examined under an epifluorescence microscope. Details of antibodies are shown in Table 2.
RT-PCR Using RT-PCR, mRNA expressions of TREK-1 and GAPDH were detected at 125 and 401 bp, respectively (Figure 1 , Lanes 2 and 3). In the negative control experiment, no product was found (Figure 1, Lane 4).
In Situ Hybridization Intense signals for TREK-1 mRNA were observed in the cytoplasm of the glomus cells by in situ hybridization (Figures 2A and 2B). Ubiquitous distribution of mRNA signals was observed in positive control section that stained with probe for poly-A sequence (Figure 2C). No signal was observed in the negative control (Figure 2D).
Immunohistochemistry Immunoreactivity for TREK-1 was observed in the rat carotid body (Figures 3A and 3B). Sections incubated with either PBS or preabsorbed antibody instead of primary antibody showed no immunoreactivity (Figure 3C). Glomus cells and nerve fibers with various thicknesses were strongly immunoreactive for TREK-1. Furthermore, dot-like structures with immunoreactivity for TREK-1 were observed around the clusters of glomus cells. Vascular endothelial cells were also immunoreactive, but fibroblasts were not immunoreactive for TREK-1.
Double Immunofluorescence Immunoreactive sites for synaptophysin, the general marker for glomus cells, were also immunoreactive for TREK-1 (Figures 4A 4C). Immunoreactive sites for GFAP, marker for sustentacular cells, and for vimentin, marker for sustentacular cells and fibroblasts, did not show TREK-1 immunoreactivity (Figures 4D4I). GFAP-immunoreactive Schwann cells were observed in the nerve bundles in the carotid body but were not immunoreactive for TREK-1. Vascular smooth muscle cells immunoreacted for ASMA were not immunoreactive for TREK-1 (Figures 4J4L).
It has been reported that TREK-1 is mainly expressed in the central nervous system at mRNA level (Medhurst et al. 2001
It has been reported that acute hypoxia occluded human TREK-1 expressed in the HEK293 cells under ischemic and/or acidotic conditions (Miller et al. 2003
On the contrary, other reports demonstrated that TREK-1 was not oxygen sensitive (Buckler and Honore 2005 In conclusion, TREK-1 would be important for K+ current modulation of the glomus cells and/or afferent nerve endings in the rat carotid body. However, two contradictory hypotheses on TREK-1 function are proposed at present. One hypothesis is that TREK-1 enhances membrane depolarization of glomus cells by hypoxic stimulation. A second hypothesis is that it is protected via phospholipids and/or arachidonic acid. To clarify the exact function of TREK-1 in the carotid body, further studies are needed.
This study was supported in part by the Grant-in-Aid for Young Scientists (B) from the Japan Society for the Promotion of Science (JSPS), Japan (15780185).
Received for publication June 13, 2005; accepted November 22, 2005
Buckler KJ, Honore E (2005) The lipid-activated two-pore domain K+ channel TREK-1 is resistant to hypoxia: implication for ischaemic neuroprotection. J Physiol 562:213222 Buckler KJ, Williams BA, Honore E (2000) An oxygen-, acid-, and anesthetic-sensitive TASK-like background potassium channel in rat arterial chemoreceptor cells. J Physiol 525:135142 Caley AJ, Gruss M, Franks NP (2005) The effects of hypoxia on the modulation of human TREK-1 potassium channels. J Physiol 562:205212 Campanucci VA, Fearon IM, Nurse CA (2003) A novel O2-sensing mechanism in rat glossopharyngeal neurons mediated by a halothane-inhibitable background K+ conductance. J Physiol 548:731743 Chemin J, Girard C, Duprat F, Lesage F, Romey G, Lazdunski M (2003) Mechanisms underlying excitatory effects of group I metabotropic glutamate receptors via inhibition of 2P domain K+ channels. EMBO J 20:54035411[CrossRef] Duprat F, Lesage F, Patel AJ, Fink M, Romey G, Lazdunski M (2000) The neuroprotective agent riluzole activates the two P domain K+ channels TREK-1 and TRAAK. Mol Pharmacol 57:906912 Hartness ME, Lewis A, Searle GJ, O'Kelly I, Peers C, Kemp PJ (2001) Combined antisense and pharmacological approaches implicate hTASK as an airway O2 sensing K+ channel. J Biol Chem 276:2649926508 Hervieu GJ, Cluderay JE, Gray CW, Green PJ, Ranson JL, Randall AD, Meadows HJ (2001) Distribution and expression of TREK-1, a two-pore-domain potassium channel, in the adult rat CNS. Neuroscience 103:899919[CrossRef][Medline] Kim D (2003) Fatty acid-sensitive two-pore domain K+ channels. Trends Pharmacol Sci 24:648654[CrossRef][Medline] Koh SD, Monagham K, Sergeant GP, Ro S, Walker RL, Sanders KM, Horowitz B (2001) TREK-1 regulation by nitric oxide and cGMP-dependent protein kinase: an essential role in smooth muscle inhibitory neurotransmission. J Biol Chem 47:4433844346 Kummer W (1997) Innervation of paraganglia. In Unsicker K, ed. AnatomicEndocrine Interactions. London, Taylor & Francis, 315356 Lauritzen I, Blondeau N, Heurteaux C, Widmann C, Romey G, Lazdunski M (2000) Polyunsaturated fatty acids are potent neuroprotectors. EMBO J 19:17841793[CrossRef][Medline] Lesage F (2003) Pharmacology of neuronal background potassium channels. Neuropharmacology 44:17[CrossRef][Medline] Maingret F, Patel AJ, Lesage F, Lazdunski M, Honoré E (2000) Lysophospholipids open the two-pore domain mechano-gated K+ channels TREK-1 and TRAAK. J Biol Chem 275:1012810133 Matsumoto I, Emori Y, Ninomiya Y, Abe K (2001) A comparative study of three cranial sensory ganglia projecting into the oral cavity: in situ hybridization analyses of neurotrophin receptors and thermosensitive cation channels. Brain Res Mol Brain Res 93:105112[Medline] Medhurst AD, Rennie G, Chapman CG, Meadows H, Duckworth MD,Kelsell RE, Gloger II, et al. (2001) Distribution analysis of human two pore domain potassium channels in tissues of the central nervous system and periphery. Brain Res Mol Brain Res 86:101114[Medline] Miller P, Kemp PJ, Lewis A, Chapman CG, Meadows HJ, Peers C (2003) Acute hypoxia occludes hTREK-1 modulation: re-evaluation of the potential role of tandem P domain K+ channels in central neuroprotection. J Physiol 548:3137 Miller P, Peers C, Kemp PJ (2004) Polymodal regulation of hTREK1 by pH, arachidonic acid, and hypoxia: physiological impact in acidosis and alkalosis. Am J Physiol Cell Physiol 286:C272282 Mizusawa A, Ogawa H, Kikuchi Y, Hida W, Kurosawa H, Okabe S, Takishima T, et al. (1994) In vivo release of glutamate in nucleus tractus solitarii of the rat during hypoxia. J Physiol 478:5566 Plant LD, Kemp PJ, Peers C, Henderson Z, Pearson HA (2002) Hypoxic depolarization of cerebellar granule neurons by specific inhibition of TASK-1. Stroke 33:23242328 Pokorski M, Strosznajder R (1993) pO2-dependence of phospholipase C in the cat carotid body. Adv Exp Med Biol 337:191195[Medline] Sanchez D, Lopez-Lopez JR, Perez-Garcia MT, Sanz-Alfayate G, Obeso A, Ganfornina MD, Gonzalez C (2002) Molecular identification of KV Strosznajder RP (1996) Acute hypoxia modulates arachidonic acid metabolism in cat carotid bodies. Role of dopamine. Acta Neurobiol Exp (Wars) 56:535543[Medline] Talley EM, Solórzano G, Lei Q, Kim D, Bayliss DA (2001) CNS distribution of members of the two-pore-domain (KCNK) potassium channel family. J Neurosci 21:74917505 Tan JH, Liu W, Saint DA (2004) Differential expression of the mechanosensitive potassium channel TREK-1 in epicardial and endocardial myocytes in rat ventricle. Exp Physiol 89:237242 Torrealba F, Bustos G, Montero VM (1996) Glutamate in the glomus cells of the cat carotid body: immunocytochemistry and in vitro release. Neurochem Int 28:625631[CrossRef][Medline] Yamamoto Y, Kummer W, Atoji Y, Suzuki Y (2002) TASK-1, TASK-2, TASK-3 and TRAAK immunoreactivities in the rat carotid body. Brain Res 950:304307[CrossRef][Medline]
This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||