MINIREVIEW
Membrane compartments and purinergic signalling: the
role of plasma membrane microdomains in the modulation
of P2XR-mediated signalling
Mikel Garcia-Marcos
1
, Jean-Paul Dehaye
2
and Aida Marino
3
1 Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA, USA
2 Laboratoire de Biochimie et de Biologie Cellulaire, Institut de Pharmacie C.P. 205 ⁄ 3, Universite
´
libre de Bruxelles, Belgium
3 Departamento de Bioquimica y Biologia Molecular, Universidad del Pais Vasco, Bilbao, Spain
ATP is the major energy reserve within cells, where its
concentration is in the millimolar range. Most of the
energy needed by the cell is obtained through hydroly-
sis of the anhydride bond between the b and the
c phosphate of the nucleotide. This canonical feature
of ATP in cellular function was probably the cause of
the scientific community’s resistance to the ‘purinergic
hypothesis’ proposed by Geoffrey Burnstock in the
early 1970s [1,2]. The regulation of cellular functions
by extracellular purines had been reported as early as
1929 [3], but the idea of ATP (and its derivatives)
working as a neurotransmitter was conceived as an
attack on the rational conservation of energy by the
cell. First, why would a cell release ATP, and second,
what would be the targets of its action? These ques-
tions have been answered to some extent by the uncov-

tors and proteases. It is poorly understood how P2XR stimulation couples
to such a variety of intracellular pathways and how the outcome from this
complex signalling network is tuned. In this context, segregation of recep-
tors and other signalling components at the plasma membrane is an attrac-
tive explanation. Lipid rafts are microdomains of biological membranes
with unique physicochemical properties that make them segregate from the
bulk of the membrane, provoking the differential partition of receptors and
signalling molecules among different domains of the plasma membrane.
Here we give an overview of the properties of lipid rafts and how they are
studied, along with recent advances in the understanding of their role in
modulating P2XR-mediated signalling.
Abbreviations
ENaC, epithelial sodium channel; ERK 1 ⁄ 2, extracellular signal-regulated kinase 1 ⁄ 2; MAP, mitogen-activated protein; N-SMase, neutral
sphingomyelinase; PKC, protein kinase C; PKD, protein kinase D; PLA
2
, phospholipase A
2
; PLC, phospholipase C; PLD, phospholipase D;
RTK, receptor tyrosine kinase.
330 FEBS Journal 276 (2009) 330–340 ª 2008 The Authors Journal compilation ª 2008 FEBS
ated through the activation of plasma membrane
receptors. Many of these receptors have been cloned
and characterized both functionally and pharmacologi-
cally [5]. Two main classes of purinergic receptors are
well characterized, i.e. P1 receptors which bind adeno-
sine, and P2 receptors which are responsive to phos-
phorylated nucleosides as ATP, ADP and other related
nucleotides [5,6]. P2 receptors have been further subdi-
vided into the P2Y and P2X subfamilies [6]. P2Y
receptors, like P1 receptors, are members of the super-

able cells (such as epithelial and immune cells). Some
remarkable functions of P2XR include regulation of
exocrine secretion, pain transmission, ion transport in
the kidney, inflammatory response, homeostasis of the
central nervous system and tumour development. A
detailed description of the tissue distribution and func-
tion of the P2X receptor in a subtype-specific way is
given in more comprehensive reviews [10,11]. The
(physio)pathological implications of this subfamily of
receptors in cellular signalling make them attractive
therapeutic targets.
The coupling between stimulation of the P2X recep-
tor and the generation of intracellular signalling
cascades is still poorly understood. Although P2XR
activation can trigger the rapid elevation of intracellu-
lar calcium ions as a second messenger, it is also cou-
pled to a number of signalling molecules (which in
many cases are not directly regulated by intracellular
calcium). It has been reported that P2XR can activate
several Ser ⁄ Thr kinases [such as protein kinase C
(PKC), Akt ⁄ protein kinase B (PKB), protein kinase D
(PKD), extracellular-signall regulated kinase 1 ⁄ 2 (ERK
1 ⁄ 2), mitogen-activated protein kinase (MAPK) p38]
[12–17], caspases [18], lipid kinases (such as phosphoi-
nositide 3-kinase) [14,17] and phospholipases (such as
PLA
2
, PLD and SMase) [19–24]. This variety of signal-
ling pathways that can be activated by the different
P2XR members raises the question about how the cor-

processes [27–30]. Recently, a definition of lipid rafts
was proposed during a Keynote Symposium on Lipid
Rafts and Cell Function held in Steamboat Springs,
CO: ‘Membrane rafts are small (10–200 nm), hetero-
geneous, highly dynamic, sterol- and sphingolipid-
enriched domains that compartmentalize cellular
processes. Small rafts can sometimes be stabilized to
form larger platforms through protein–protein and
M. Garcia-Marcos et al. P2X receptors and membrane microdomains
FEBS Journal 276 (2009) 330–340 ª 2008 The Authors Journal compilation ª 2008 FEBS 331
protein–lipid interactions’ [31]. By extension, lipid
rafts could be defined as localized rigid regions within
the bulk of fluid membrane and which are enriched in
cholesterol and (glycero-)sphingolipids. In addition the
fatty acid chains of the phospholipids composing
these rigid domains are generally more saturated than
those in the lipids of the surrounding membrane. In
fact, this fatty acid composition favors a tighter pack-
ing of phospholipids and cholesterol, increasing the
rigidity of these domains [32–35]. This composition
accounts for their insolubility in non-ionic detergents,
a hallmark that has been used as an ‘operational defi-
nition’ of these domains and which has been exploited
to study them from a biochemical point of view (see
below) [29,35,36]. Probably the most relevant reason
for the implication of lipid rafts in the signalling pro-
cess is that they can contain or exclude proteins such
as receptors, transducer ⁄ adaptor proteins and effec-
tors, which are directly involved in signal transduction
[35,37,38]. The clustering of signalling molecules

plasma membrane [27,29]. Thus, the proposal that
membranes in a cell could be segregated into domains
with different properties and resistance to solubiliza-
tion by non-ionic detergents was initially established
as an operational definition of lipid rafts. The use of
this general biochemical approach has not been with-
out controversy [43]. The existence of lipid rafts was
questioned and some naysayers pretended they were
merely an artefactual consequence of the methodology
used to isolate them. The existence of lipid rafts
in vivo is now supported by a number of studies. For
example, it has been shown by direct live cell micros-
copy that ‘raft-resident’ clusters of proteins segregate
from ‘non-raft’ proteins in the cell membrane [44–46].
The same technique combined with the use of Laur-
dan as a fluorescent probe has also demonstrated that
the lipid components of the membrane can segregate
into domains with different physical properties (i.e.
more versus less ordered) [47]. The use of immuno-
electron microscopy has been another interesting
approach to quantify the degree of clustering of mole-
cules in ‘ripped-off’ plasma membrane sheets [48–50].
Using this technique, several protein and lipid markers
have been studied for their ability to cluster in
response to extracellular stimuli and the size of the
domains containing those clusters has been estimated.
In summary, multiple lines of evidence have helped to
argue in favour of the existence of lipid rafts in cell
membranes and the use of detergent-resistance and
other alternatives (see below) as a biochemical

another common method is performed in neutral pH
buffers but includes several density-gradient steps to
obtain the desired purified fraction [53]. More recently,
a simplified version of the latter protocol was
described by MacDonald and Pike, which yields a
membrane fraction enriched in lipid raft markers by a
one-step density gradient ultracentrifugation [54].
Methods developed to specifically isolate caveolae and
not other membrane microdomains have also been
developed. Oh and Schnitzer used the silica-coating
technique originally described for the isolation of
endothelial membranes to subsequently disrupt them
and obtain a caveolar fraction by floatation in a den-
sity gradient [55,56]. Immunoisolation of the caveolar
fraction from a detergent-resistant preparation of
membranes using caveolin Ig has also been successful
[57].
None of the methods described above is flawless and
the best way to achieve a meaningful result is by per-
forming rigorous controls and using complementary
approaches to validate the results. For example,
detergent-based methods can abolish the interaction of
proteins weakly associated with lipid rafts or provoke
the loss of raft proteins that also tightly bind to cyto-
skeletal components. The detergent extraction condi-
tions can also lead to the artefactual formation of
membrane domains and promote lipid mixing between
different membrane fractions [42,51]. ‘Detergent-free’
methods might seem to interfere less with the native
properties of the membranes, but are less reproducible

regulate the duration of a response. Lipid rafts ⁄ caveo-
lae have been shown to be implicated in a myriad of
signalling pathways. For example, receptor tyrosine
kinase (RTK) for epidermal growth factor, insulin,
nerve growth factor or platelet-derived growth factor
have been shown to localize to lipid rafts [59–61].
However, upon stimulation with the respective agon-
ists, the localization of these receptors with regard to
raft versus non-raft domains varies from case to case,
implying different mechanisms of regulation. A sub-
stantial number of studies have investigated Ras sig-
nalling in the context of lipid rafts. Ras is a small
GTPase that is activated downstream of many RTKs
and mediates signalling to MAPK and phosphatidyl-
inositol 3-kinase from the plasma membrane. Specifi-
cally, the H-ras isoform is recruited to lipid rafts upon
activation, which triggers intracellular signalling
[49,62]. Another molecule that mediates signalling
from RTKs and is found in lipid rafts is the lipid
phosphatidylinositol 4,5-bisphosphate [63,64]. This is a
substrate for both PLCc and phosphatidylinositol
3-kinase, two enzymes usually coupled to RTKs. The
intermediate phosphatidylinositol 4,5-bisphosphate is
also shared with certain signalling pathways coupled
to GPCRs. Many members of this family of receptors
(b-adrenergic receptors, muscarinic receptors, endo-
thelin receptors, rhodopsin) are located in lipid rafts
[65–70] where they are in close proximity to their
transducing GTP-binding protein (Gs, Gi, Go, Gq and
transducin alpha subunits) [53,69,71–73] and to some

2
receptors have also been mor-
phologically localized to caveolae at least in placenta
[80]. In platelets, the P2Y
12
-mediated decrease in
cAMP levels is sensitive to lipid raft disruption [81,82].
This receptor forms functional homo-oligomers in
platelet membrane rafts; clopidogrel (an antithrom-
botic drug) and its active compound derivative prob-
ably block the P2Y
12
receptor by disassembling these
oligomers and displacing them to non-raft domains
[82]. In contrast to these results, the depletion of
cholesterol by methyl-b-cyclodextrins does not affect
the increase of calcium levels in response to the activa-
tion of platelet P2Y
1
receptors [83].
As previously mentioned, P2X receptors are not
coupled to G proteins but form non-selective cation
channels with structural similarities to the sodium
channels encoded by the ENaC ⁄ degenerins gene [84].
Some voltage-regulated ion channels have been
reported to function via lipid rafts [85], a property
shared with some ligand-gated channels like nicotinic,
AMPA, NMDA, GABA and ATP receptors [86].
However, localization in membrane microdomains is
not a general property of P2X receptors and the exper-

receptor
could be isolated in raft fraction prepared by a deter-
gent-free protocol but increasing concentrations of
Triton X-100 (0.1–1%) led to a shift of the protein to
high-density detergent-soluble fractions [88]. This
receptor was found in lipid rafts when heterologously
expressed in HEK 293 cells or when investigated in
smooth muscle cells and platelets that constitutively
express the receptor. Disruption of lipid rafts by
Table 1. P2XR localization in lipid rafts ⁄ caveolae. ND, not determined.
Receptor
Method used to isolate lipid
rafts ⁄ caveolae
Also found
in the non-raft
fraction?
a
Effect on P2XR function
observed upon lipid raft
disruption Ref.Detergent-based Detergent-free
P2X
1
No
b
Yes No Blockade of receptor-mediated
currents and artery contraction
[83,88]
P2X
2
No ND – –

conditions (Brij 95 instead of Triton X-100) are used.
P2X receptors and membrane microdomains M. Garcia-Marcos et al.
334 FEBS Journal 276 (2009) 330–340 ª 2008 The Authors Journal compilation ª 2008 FEBS
cholesterol depletion delocalized P2X
1
receptors out of
lipid rafts and greatly impaired the increase in intra-
cellular calcium concentrations and the muscle con-
traction in response to receptor occupancy [88]. As for
the P2X
3
receptor, no translocation upon receptor acti-
vation could be observed. More recently, Barth and
colleagues reported that only a minor fraction of the
P2X
4
receptors of lung epithelial cells were located in
rafts isolated with 1% Triton X-100 but that these
receptors were prominently in lipid rafts prepared with
Brij-95, a less stringent detergent. Interestingly, in
these cells the P2X
4
receptor expression and recruit-
ment to raft fractions were promoted upon ATP stim-
ulation [89]. However the role of P2X receptor
partition between different membrane domains in the
coupling to specific downstream signalling pathways is
still poorly understood. In this regard, some informa-
tion has been made available for the P2X
7

7
receptor to caveolae is critical for its nor-
mal turnover in the cell [92]. In addition, the same
group has recently observed that the P2X
7
receptor
can form a protein complex with caveolin-1 [89]. This
supports the idea that the P2X
7
receptor localizes to
lipid rafts ⁄ caveole via a protein–protein interaction
that might be destabilized by detergent extraction dur-
ing lipid raft isolation. Moreover, these studies have
provided some insights into the significance of the
localization of the P2X
7
receptors in lipid rafts regard-
ing the regulation of intracellular signalling pathways.
Interestingly, the P2X
7
receptor is a substrate for
ART 2.2, a glycosylphosphatidylinositol-anchored ADP-
ribosyltransferase that is also enriched in lipid rafts
[90]. The fact that the P2X
7
can be activated by ADP-
ribosylation as an alternative to ligand binding [93,94],
strongly suggests that the receptors localized in lipid
rafts could be biased to this alternative way of activa-
tion which in turn could activate a specific downstream

nal end [95,96]. These features raise the possibility that
the localization of the P2X
7
receptor to lipid rafts pro-
motes its interaction with proteins coupled to specific
signalling pathways.
Given that both P2X and other purinergic receptors
(i.e. P1 and P2Y) can localize differentially in microdo-
mains of the plasma membrane, the topology of puri-
nergic receptors is important for modulating signalling
triggered by P2X receptors, and also for its integration
with other purinergic signalling events (Fig. 1). Extra-
cellular levels of nucleotides are regulated by ectonu-
cleotidases [97]. Considering the exquisite specificity of
different purinergic receptors for different purinergic
compounds [6], this extracellular processing of nucleo-
tides is crucial in determining the final cellular
response. The ATP released to the media could act on
P2X receptors but once degraded to ADP the signal-
ling would shift to P2Y receptors and in a similar fash-
ion to P1 receptors once adenosine is generated by
subsequent enzymatic processing. Nucleotides can be
hydrolysed by enzymes with a broad spectrum of sub-
strates, such as ecto-alkaline phosphatases (hydrolysis
of nucleoside-5¢-tri-, di- and monophosphates) or ecto-
5¢-nucleotidases (hydrolysis of nucleoside-5¢-mono-
phosphates) [97]. Interestingly, these enzymes are not
localized randomly at the plasma membrane but are
M. Garcia-Marcos et al. P2X receptors and membrane microdomains
FEBS Journal 276 (2009) 330–340 ª 2008 The Authors Journal compilation ª 2008 FEBS 335

partmentalized entity that organizes the signal trans-
duction machinery serves as a hypothesis to explain
part of this complex process. In the case of P2XR, this
plasma membrane compartmentalization seems to
determine coupling to different signalling pathways. In
addition, it also seems to contribute to the fine-tuning
of P2XR-mediated signalling by controlling the local
kinetics of extracellular agonist degradation and the
integration with different purinergic signal inputs (via
other purinoceptors such as P2Y or P1) to generate
the final cellular response. Further investigation of this
topic might shed light on some controversial or unre-
solved issues regarding purinergic signalling [103], such
as the functional interaction of multiple receptors in
Fig. 1. Schematic diagram of how the topological distribution of purinergic signalling components might regulate the final cellular response.
P2XR have been described as being localized in both raft and non-raft membrane fractions and to couple to different downstream signalling
pathways depending on their location once activated by ATP. The enrichment of ecto-nucleotidases in lipid rafts would promote the acceler-
ated degradation of ATP to ADP and adenosine in the periphery of these microdomains. ADP and adenosine would activate respectively P2Y
and P1 receptors which are localized in lipid rafts and would engage their respective signalling pathways through G proteins. The differential
localization of receptors and ecto-nucleotidases would modulate the input signals in the form of ATP or its degradation products, as well as
the specific intracellular signalling outputs from each subclass of receptors. Finally, all these different intracellular signalling outputs would
be integrated to provoke the cellular response.
P2X receptors and membrane microdomains M. Garcia-Marcos et al.
336 FEBS Journal 276 (2009) 330–340 ª 2008 The Authors Journal compilation ª 2008 FEBS
single cells or the complex responses associated to
some receptors like the P2X
7
.
Acknowledgements
This work was supported by grant no. 3.4.528.07.F

surface ATP sensors in health and disease. Nature 442,
527–532.
9 Denlinger LC, Fisette PL, Sommer JA, Watters JJ,
Prabhu U, Dubyak GR, Proctor RA & Bertics PJ
(2001) Cutting edge: the nucleotide receptor P2X7 con-
tains multiple protein- and lipid-interaction motifs
including a potential binding site for bacterial lipopoly-
saccharide. J Immunol 167, 1871–1876.
10 Burnstock G & Knight GE (2004) Cellular distribution
and functions of P2 receptor subtypes in different
systems. Int Rev Cytol 240, 31–304.
11 Koles L, Furst S & Illes P (2007) Purine ionotropic
(P2X) receptors. Curr Pharm Des 13, 2368–2384.
12 Heo JS & Han HJ (2006) ATP stimulates mouse
embryonic stem cell proliferation via protein kinase C,
phosphatidylinositol 3-kinase ⁄ Akt, and mitogen-acti-
vated protein kinase signaling pathways. Stem Cells 24,
2637–2648.
13 da Cruz CM, Ventura AL, Schachter J, Costa-Junior
HM, da Silva Souza HA, Gomes FR, Coutinho-Silva
R, Ojcius DM & Persechini PM (2006) Activation of
ERK1 ⁄ 2 by extracellular nucleotides in macrophages is
mediated by multiple P2 receptors independently of
P2X7-associated pore or channel formation. Br J Phar-
macol 147, 324–334.
14 Cruz CM, Rinna A, Forman HJ, Ventura AL, Perse-
chini PM & Ojcius DM (2007) ATP activates a reactive
oxygen species-dependent oxidative stress response and
secretion of proinflammatory cytokines in macrophag-
es. J Biol Chem 282, 2871–2879.

pools of P2X7 receptors to distinct intracellular signal-
ing pathways in rat submandibular gland. J Lipid Res
47, 705–714.
22 Alzola E, Perez-Etxebarria A, Kabre E, Fogarty DJ,
Metioui M, Chaib N, Macarulla JM, Matute C,
Dehaye JP & Marino A (1998) Activation by P2X7
agonists of two phospholipases A
2
(PLA
2
) in ductal
cells of rat submandibular gland. Coupling of the
calcium-independent PLA2 with kallikrein secretion.
J Biol Chem 273, 30208–30217.
23 Andrei C, Margiocco P, Poggi A, Lotti LV, Torrisi
MR & Rubartelli A (2004) Phospholipases C and A
2
control lysosome-mediated IL-1 beta secretion: implica-
tions for inflammatory processes. Proc Natl Acad Sci
USA 101, 9745–9750.
24 Lee YH, Lee SJ, Seo MH, Kim CJ & Sim SS (2001)
ATP-induced histamine release is in part related to
phospholipase A
2
-mediated arachidonic acid metabo-
M. Garcia-Marcos et al. P2X receptors and membrane microdomains
FEBS Journal 276 (2009) 330–340 ª 2008 The Authors Journal compilation ª 2008 FEBS 337
lism in rat peritoneal mast cells. Arch Pharm Res 24,
552–556.
25 Singer SJ & Nicolson GL (1972) The fluid mosaic

seas. Biochem J 378, 281–292.
37 Simons K & Toomre D (2000) Lipid rafts and signal
transduction. Nat Rev Mol Cell Biol 1, 31–39.
38 Insel PA, Head BP, Ostrom RS, Patel HH, Swaney
JS, Tang CM & Roth DM (2005) Caveolae and lipid
rafts: G protein-coupled receptor signaling microdo-
mains in cardiac myocytes. Ann NY Acad Sci 1047,
166–172.
39 Palade GE (1953) The fine structure of blood capillar-
ies. J Appl Phys 24, 1424.
40 Glenney JR Jr & Soppet D (1992) Sequence and
expression of caveolin, a protein component of caveo-
lae plasma membrane domains phosphorylated on
tyrosine in Rous sarcoma virus-transformed fibroblasts.
Proc Natl Acad Sci USA 89, 10517–10521.
41 Monier S, Parton RG, Vogel F, Behlke J, Henske A &
Kurzchalia TV (1995) VIP21-caveolin, a membrane
protein constituent of the caveolar coat, oligomerizes
in vivo and in vitro. Mol Biol Cell 6, 911–927.
42 Lichtenberg D, Goni FM & Heerklotz H (2005) Deter-
gent-resistant membranes should not be identified with
membrane rafts. Trends Biochem Sci 30, 430–436.
43 Munro S (2003) Lipid rafts: elusive or illusive? Cell
115, 377–388.
44 Varma R & Mayor S (1998) GPI-anchored proteins
are organized in submicron domains at the cell surface.
Nature 394, 798–801.
45 Harder T, Scheiffele P, Verkade P & Simons K (1998)
Lipid domain structure of the plasma membrane
revealed by patching of membrane components. J Cell

A detergent-free method for purifying caveolae mem-
brane from tissue culture cells. Proc Natl Acad Sci
USA 92, 10104–10108.
54 Macdonald JL & Pike LJ (2005) A simplified method
for the preparation of detergent-free lipid rafts. J Lipid
Res 46, 1061–1067.
55 Schnitzer JE, McIntosh DP, Dvorak AM, Liu J & Oh
P (1995) Separation of caveolae from associated micr-
odomains of GPI-anchored proteins. Science 269,
1435–1439.
56 Liu J, Oh P, Horner T, Rogers RA & Schnitzer JE
(1997) Organized endothelial cell surface signal trans-
duction in caveolae distinct from glycosylphosphat-
idylinositol-anchored protein microdomains. J Biol
Chem 272, 7211–7222.
57 Oh P & Schnitzer JE (1999) Immunoisolation of caveo-
lae with high affinity antibody binding to the oligo-
P2X receptors and membrane microdomains M. Garcia-Marcos et al.
338 FEBS Journal 276 (2009) 330–340 ª 2008 The Authors Journal compilation ª 2008 FEBS
meric caveolin cage. Toward understanding the basis
of purification. J Biol Chem 274, 23144–23154.
58 Foster LJ, De Hoog CL & Mann M (2003) Unbiased
quantitative proteomics of lipid rafts reveals high speci-
ficity for signaling factors. Proc Natl Acad Sci USA
100, 5813–5818.
59 Mineo C, Gill GN & Anderson RG (1999) Regulated
migration of epidermal growth factor receptor from
caveolae. J Biol Chem 274, 30636–30643.
60 Huang CS, Zhou J, Feng AK, Lynch CC, Klumper-
man J, DeArmond SJ & Mobley WC (1999) Nerve

J Biol Chem 277, 34280–34286.
68 Feron O, Smith TW, Michel T & Kelly RA (1997)
Dynamic targeting of the agonist-stimulated m2 musca-
rinic acetylcholine receptor to caveolae in cardiac
myocytes. J Biol Chem 272, 17744–17748.
69 Seno K, Kishimoto M, Abe M, Higuchi Y, Mieda M,
Owada Y, Yoshiyama W, Liu H & Hayashi F (2001)
Light- and guanosine 5¢-3-O-(thio)triphosphate-sensi-
tive localization of a G protein and its effector on
detergent-resistant membrane rafts in rod photorecep-
tor outer segments. J Biol Chem 276, 20813–20816.
70 Chun M, Liyanage UK, Lisanti MP & Lodish HF
(1994) Signal transduction of a G protein-coupled
receptor in caveolae: colocalization of endothelin and
its receptor with caveolin. Proc Natl Acad Sci USA 91,
11728–11732.
71 Sargiacomo M, Sudol M, Tang Z & Lisanti MP
(1993) Signal transducing molecules and glycosyl-
phosphatidylinositol-linked proteins form a caveolin-
rich insoluble complex in MDCK cells. J Cell Biol
122, 789–807.
72 Huang C, Hepler JR, Chen LT, Gilman AG, Anderson
RG & Mumby SM (1997) Organization of G proteins
and adenylyl cyclase at the plasma membrane. Mol
Biol Cell 8, 2365–2378.
73 Oh P & Schnitzer JE (2001) Segregation of heterotri-
meric G proteins in cell surface microdomains. G(q)
binds caveolin to concentrate in caveolae, whereas G(i)
and G(s) target lipid rafts by default. Mol Biol Cell 12,
685–698.

Eur J Histochem 48, 253–259.
81 Quinton TM, Kim S, Jin J & Kunapuli SP (2005)
Lipid rafts are required in Galpha(i) signaling down-
stream of the P2Y12 receptor during ADP-mediated
platelet activation. J Thromb Haemost 3, 1036–1041.
82 Savi P, Zachayus JL, Delesque-Touchard N, Labouret
C, Herve C, Uzabiaga MF, Pereillo JM, Culouscou
JM, Bono F, Ferrara P et al. (2006) The active metab-
olite of Clopidogrel disrupts P2Y12 receptor oligomers
M. Garcia-Marcos et al. P2X receptors and membrane microdomains
FEBS Journal 276 (2009) 330–340 ª 2008 The Authors Journal compilation ª 2008 FEBS 339
and partitions them out of lipid rafts. Proc Natl Acad
Sci USA 103, 11069–71104.
83 Vial C, Fung CY, Goodall AH, Mahaut-Smith MP &
Evans RJ (2006) Differential sensitivity of human
platelet P2X1 and P2Y1 receptors to disruption of lipid
rafts. Biochem Biophys Res Commun 343, 415–419.
84 Kellenberger S & Schild L (2002) Epithelial sodium
channel ⁄ degenerin family of ion channels: a variety of
functions for a shared structure. Physiol Rev 82, 735–
767.
85 Szabo I, Adams C & Gulbins E (2004) Ion channels
and membrane rafts in apoptosis. Pflugers Arch 448,
304–312.
86 Allen JA, Halverson-Tamboli RA & Rasenick MM
(2007) Lipid raft microdomains and neurotransmitter
signalling. Nat Rev Neurosci 8, 128–140.
87 Vacca F, Amadio S, Sancesario G, Bernardi G &
Volonte C (2004) P2X3 receptor localizes into lipid
rafts in neuronal cells. J Neurosci Res 76, 653–661.

actors in cell communication and signaling. Curr Med
Chem 11, 857–872.
95 Kim M, Jiang LH, Wilson HL, North RA & Surpre-
nant A (2001) Proteomic and functional evidence for a
P2X7 receptor signalling complex. EMBO J 20, 6347–
6358.
96 Wilson HL, Wilson SA, Surprenant A & North RA
(2002) Epithelial membrane proteins induce membrane
blebbing and interact with the P2X7 receptor C termi-
nus. J Biol Chem 277, 34017–34023.
97 Zimmermann H (2000) Extracellular metabolism of
ATP and other nucleotides. Naunyn Schmiedebergs
Arch Pharmacol 362, 299–309.
98 Kenworthy AK & Edidin M (1998) Distribution of a
glycosylphosphatidylinositol-anchored protein at the
apical surface of MDCK cells examined at a resolution
of < 100 A
˚
using imaging fluorescence resonance
energy transfer. J Cell Biol 142, 69–84.
99 Kukulski F, Levesque SA, Lavoie EG, Lecka J, Bigon-
nesse F, Knowles AF, Robson SC, Kirley TL & Sev-
igny J (2005) Comparative hydrolysis of P2 receptor
agonists by NTPDases 1, 2, 3 and 8. Purinergic Signal
1, 193–204.
100 Kittel A, Kaczmarek E, Sevigny J, Lengyel K, Csizm-
adia E & Robson SC (1999) CD39 as a caveolar-asso-
ciated ectonucleotidase. Biochem Biophys Res Commun
262, 596–599.
101 Koziak K, Kaczmarek E, Kittel A, Sevigny J, Blus-