Recombinant Rat P2Y purinoceptor 4 (P2ry4)

What is rat P2Y4 purinoceptor and how does it differ from other P2Y receptors?

The rat P2Y4 receptor (rP2Y4) is a G protein-coupled metabotropic receptor that responds to extracellular nucleotides. It belongs to the P2Y receptor family which, along with P2X receptors (ligand-gated ion channels), constitute the main classes of purinergic receptors .

Key distinguishing characteristics:

• rP2Y4 is primarily coupled to Gαq proteins, leading to PLC activation, IP3 generation, and intracellular Ca2+ mobilization

• Unlike some other P2Y subtypes (P2Y1, P2Y12, P2Y13), rP2Y4 responds equally well to both ATP and UTP

• The receptor shows distinctive pharmacological profiles compared to other P2Y subtypes, including unique responses to antagonists like Reactive Blue 2 (RB-2)

Methodological approach for identification: RT-PCR using specific primers for P2Y4 represents the standard method for identifying expression at the mRNA level. For example, primers designed based on published rat P2Y4 sequences from GenBank can be used with appropriate annealing temperatures (typically around 60°C) .

How does rat P2Y4 receptor differ from human P2Y4 receptor?

Despite >80% amino acid sequence identity, rat and human P2Y4 receptors exhibit significant pharmacological differences:

This species difference is significant and highlights that findings from rat models cannot be directly extrapolated to human P2Y4 function .

Methodological consideration: When designing experiments, researchers must consider these species-specific pharmacological differences, particularly when using nucleotide analogs or antagonists, as they may have different effects in rat versus human receptors .

What are the primary agonists and antagonists for rat P2Y4 receptors?

Agonist profile:

Antagonist profile:

Methodological approach: When designing pharmacological experiments, researchers should use multiple selective compounds to verify receptor identity. The differential responses to RB-2, BzATP, and ATPγS can help distinguish rP2Y4 from rP2Y2 receptors .

What experimental methods can reliably distinguish between rat P2Y2 and rat P2Y4 receptors?

Since rat P2Y2 and P2Y4 receptors show similar responses to ATP and UTP, distinguishing between them requires multiple complementary approaches:

• Differential nucleotide potency:

  • Test CTP, GTP and especially ITP, which shows 13-fold selectivity for P2Y4 over P2Y2

  • Test dinucleotides: P2Y4 is fully activated only by Ap4A, while P2Y2 responds to multiple dinucleotides (Ap3A, Ap4A, Ap5A, Ap6A)

• Antagonist profiling:

  • RB-2 is a competitive antagonist at P2Y4 (pA2 = 6.43) but much less potent at P2Y2

  • Suramin potently blocks P2Y2 but is much less effective at P2Y4

• Modulation by extracellular factors:

  • pH sensitivity: Acidification (pH 5.5-8.0) enhances agonist potency 8-10 fold at P2Y4 but not at P2Y2

  • Zinc sensitivity: Extracellular Zn2+ (0.1-300 μM) inhibits P2Y4 but not P2Y2 responses

• Synthetic nucleotide responses:

  • BzATP activates P2Y2 but inhibits P2Y4

  • ATPγS fully activates P2Y2 but only weakly activates P2Y4

Experimental design recommendation: Researchers should use a combination of these approaches rather than relying on a single pharmacological tool to definitively identify the receptor subtype .

What is the expression pattern of P2Y4 receptors in rat tissues?

P2Y4 receptor expression has been detected in various rat tissues with specific distribution patterns:

Methodological consideration: Expression levels can vary with tissue preparation methods and culture conditions. For instance, P2Y4 mRNA expression in hepatocytes decreased significantly after overnight culture compared to freshly isolated cells .

How can researchers effectively detect P2Y4 receptor expression in tissue samples?

Multiple complementary techniques should be employed for comprehensive detection:

• mRNA detection:

  • RT-PCR using specific primers (see primer sequences in search result )

  • RT-qPCR with normalization to stable reference genes (e.g., RPL4)

  • In situ hybridization for spatial distribution within tissues

• Protein detection:

  • Immunohistochemistry using validated antibodies

  • Western blotting for quantification

  • For specificity controls: preadsorption with blocking peptides and primary antibody omission

• Functional assays:

  • Ca2+ imaging with selective agonists/antagonists

  • Electrophysiological recordings with pharmacological profiling

Methodological recommendation: Include appropriate controls for antibody specificity, such as preadsorption with blocking peptides and primary antibody omission controls. For nucleotide-based functional assays, include P2Y4-selective pharmacological tools to distinguish from other P2 receptors .

What are the primary signaling pathways activated by rat P2Y4 receptors?

The rat P2Y4 receptor primarily couples to Gαq/11 proteins, initiating the following signaling cascade:

• Primary signaling pathway:

  • Activation of phospholipase C (PLC)

  • Generation of inositol 1,4,5-trisphosphate (IP3)

  • IP3-mediated Ca2+ release from intracellular stores

  • Subsequent activation of Ca2+-dependent processes

• Secondary effectors:

  • Activation of Ca2+-activated K+ channels (in neurons)

  • Protein kinase C (PKC) activation

  • Modulation by phosphatidylinositol 4,5-bisphosphate (PIP2)

• Unique signaling characteristics:

  • Unlike P2Y1-mediated Ca2+ oscillations, P2Y4-linked Ca2+ oscillations are less sensitive to negative regulation by PKC

  • P2Y4-linked Ca2+ oscillations are independent of Ca2+ influx, unlike P2Y1-linked responses

Methodological approach: To characterize these pathways, researchers can use:

• Fura-2 loaded cells for Ca2+ imaging

• Perforated patch whole-cell recordings to measure associated currents

• Pharmacological inhibitors of PLC (U73122), IP3 receptors (2-APB), or PKC (GF109203X, Ro-31-8220)

How do extracellular factors modulate rat P2Y4 receptor function?

Several extracellular factors significantly modulate rat P2Y4 receptor function:

Experimental design considerations:

• When studying P2Y4 function, buffer pH should be carefully controlled and reported

• Zinc contamination from glassware or water sources should be minimized or controlled

• For comparative studies between P2Y subtypes, these modulatory effects can be exploited as differentiating tools

What techniques are recommended for heterologous expression and characterization of recombinant rat P2Y4?

For successful heterologous expression and characterization of rat P2Y4:

• Expression systems:

  • Xenopus oocytes: Ideal for electrophysiological studies and pharmacological characterization

  • Mammalian cell lines: 1321N1 cells (lacks endogenous P2 receptors), HEK293, or Jurkat cells

  • Expression vector recommendations: pCDNA3.1 or pEGFP-N1 for mammalian cells; pGEMHE for oocytes

• Transfection/Expression methods:

  • For oocytes: Microinjection of cRNA (typically 5-10 ng/oocyte)

  • For mammalian cells: Lipofection, calcium phosphate precipitation, or electroporation

  • Verification of expression: RT-PCR, Western blotting, or reporter-tagged constructs

• Functional characterization:

  • Two-electrode voltage clamp (for oocytes)

  • Calcium imaging using ratiometric dyes (Fura-2)

  • Inositol phosphate accumulation assays

  • Patch-clamp electrophysiology for associated currents

Methodological recommendation: When expressing P2Y4 receptors for pharmacological studies, researchers should adjust cRNA/cDNA amounts to achieve similar expression levels when comparing multiple receptor subtypes. This helps minimize the impact of receptor reserve on agonist potency measurements .

What is known about the role of P2Y4 receptors in developmental processes?

Studies in Xenopus embryos have revealed critical developmental functions of P2Y4 receptors:

• Head formation:

  • P2Y4 depletion using TALEN-mediated knockout results in small head phenotypes

  • Disruption affects expression of neural crest marker snail1

  • Reduces expression of neural plate marker sox2 in the anterior region

  • Decreases expression of fore-midbrain marker otx2, retinal markers pax6/rx1, and hindbrain marker krox20

• Gastrulation and morphogenetic movements:

  • P2Y4 disruption affects mesoderm involution during gastrulation

  • Can result in spina bifida phenotype

  • Distinct from P2Y11 which affects convergent extension but not involution

• Head organizer function:

  • P2Y4 is required for expression of head organizer genes (dkk1 and cer)

  • Necessary but not sufficient for head organizer formation

Methodological approach for developmental studies: TALEN-mediated gene disruption, in situ hybridization for expression analysis of developmental markers, and rescue experiments with mRNA injection can be employed to study P2Y4 function in development .

How can researchers distinguish between P2Y4 receptor-mediated effects and those of other purinergic receptors in complex systems?

Distinguishing P2Y4-mediated effects in complex biological systems requires multiple complementary approaches:

• Pharmacological differentiation strategy:

  • Use P2Y4-preferring agonist profiles: equal sensitivity to ATP, UTP, CTP, GTP, and ITP is characteristic of P2Y4

  • Apply selective antagonist patterns: RB-2 sensitivity combined with relative suramin resistance

  • Employ modulatory effects: test pH sensitivity (8-10 fold enhancement at acidic pH) and Zn2+ inhibition

• Genetic approaches:

  • RNA interference (siRNA or shRNA) for selective knockdown

  • CRISPR/Cas9 or TALEN-mediated gene editing

  • Antisense oligonucleotides targeted to P2Y4-specific sequences

• Expression correlation:

  • Correlate functional responses with P2Y4 expression levels across tissues

  • Use single-cell approaches to link receptor expression with functional readouts

• Combinatorial exclusion:

  • Systematically eliminate other purinergic subtypes using selective tools

  • For example, use MRS2500 to block P2Y1, AR-C118925XX for P2Y2, MRS2578 for P2Y6, etc.

  • Complement with P2X blockers (TNP-ATP, PPADS) to eliminate ionotropic responses

Methodological recommendation: Researchers should employ at least two independent approaches (pharmacological and genetic) to confirm P2Y4-specific effects in complex systems where multiple purinergic receptors are expressed .

What are the current knowledge gaps and future research directions for rat P2Y4 receptors?

Despite significant advances in our understanding of P2Y4 receptors, several knowledge gaps remain:

• Structural aspects:

  • Crystal structure of P2Y4 has not been resolved, unlike some other P2Y receptors

  • Detailed understanding of ligand binding sites and gating mechanisms remains incomplete

  • Structure-based drug design targeting P2Y4 is limited by this knowledge gap

• Physiological roles:

  • Specific functions in different tissues remain incompletely characterized

  • Exact contribution to purinergic signaling in co-expression contexts with other P2 receptors

  • Detailed understanding of developmental roles beyond initial characterization

• Pathophysiological significance:

  • Potential contributions to inflammatory processes

  • Possible roles in neuropathic pain similar to P2X4

  • Involvement in developmental disorders associated with defective head formation

Future research directions:

• Development of truly selective pharmacological tools for P2Y4

• Generation and characterization of tissue-specific conditional knockout models

• Exploration of potential therapeutic applications by targeting P2Y4 in specific pathologies

• Investigation of potential hetero-oligomerization with other P2Y or G protein-coupled receptors