Key result
In addition to P2y and P2U receptors, cardiac endothelial cells possess a distinct pyrimidine receptor that responds to UTP but not purine nucleotides to liberate intracellular calcium.
Demonstrates the presence of a discrete UTP receptor in cardiac endothelial cells that liberates intracellular calcium via a G-protein.
Answers are grounded in this paper and cite their sources.
No immediate clinical implications; leaves open the role of UTP-specific receptors in human cardiac endothelium.
We have examined the effects of various purine and pyrimidine nucleotides upon cells cultured from guinea-pig cardiac endothelium (CEC), and find the P2Y-agonist 2-methylthioadenosine triphosphate (2MeSATP) to be a potent (EC50 = 85 +/- 10.2 nM) stimulator of increase in intracellular calcium concentrations, while uridine 5'-triphosphate (UTP) and adenosine 5'-triphosphate (ATP) are less potent but equipotent with one another (EC50s = 2.1 +/- 0.3 and 1.8 +/- 0.2 microM, respectively). 2. While the P2Y receptor exhibited rapid homologous desensitization, this had no effect upon subsequent responsiveness of CEC to either ATP or UTP. Effects of maximal concentrations of ATP and UTP were not only additive, but did not cross-desensitize. Responses to UTP (but not to ATP or 2MeSATP) were blocked by treatment with pertussis toxin (PTX); all three nucleotides appeared to liberate calcium from an intracellular pool. 3. Suramin (30 microM) significantly (P < 0.05) increased the EC50 for ATP-dependent increases in intracellular calcium (5.3 +/- 2.2 microM vs. 2.0 +/- 0.9 microM in the absence of suramin), while it completely blocked the response to 2MeSATP. Suramin had no effect upon responses to UTP at concentrations of 100 microM. 4. We conclude that in addition to the P2Y and P2U subtypes of the ATP receptor, an additional receptor responsive to UTP but exhibiting no affinity for purine nucleotides is present in CEC; this "pyrimidine receptor' liberates intracellular calcium via a G-protein, and may partly mediate the contractile response to UTP in the coronary vasculature.
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Buxton et al. (1996) studied this question. Uridine 5'-triphosphate (UTP) vs. Adenosine 5'-triphosphate (ATP) and 2MeSATP was evaluated on Increase in intracellular calcium concentration. In addition to P2y and P2U receptors, cardiac endothelial cells possess a distinct pyrimidine receptor that responds to UTP but not purine nucleotides to liberate intracellular calcium.
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