P2Y 11 receptor expression by human lymphocytes: evidence for two cAMP-linked purinoceptors

Abstract

The effects of extracellular ATP, ADP, AMP and adenosine on cAMP accumulation have been studied in freshly isolated B-lymphocytes from patients with chronic lymphocytic leukemia. Extracellular ATP and several nucleotide analogs stimulated cAMP accumulation with the following order of potency: ATP (EC 50=120±20 μM)>ADP≫AMP. ADP was less effective than ATP and may be a partial agonist. AMP exhibited variable but generally weak activity. The stable analog of ATP, α,β-methylene ATP (EC 50=110±15 μM) also stimulated cAMP accumulation and exhibited similar efficacy to ATP. The P2Y 2 receptor agonist, UTP had no effect on intracellular cAMP levels. Adenosine and the A 2A/A 2B receptor agonist, 5′- N-ethylcarboxamidoadenosine (NECA) also stimulated cAMP accumulation in CLL lymphocytes. Adenosine deaminase inhibited the cAMP response to adenosine but had no effect on the ATP-induced cAMP response. On the other hand, the AMP analog, adenosine 5′-thiomonophosphate, (AMPS; 1.0 mM) inhibited ATP-induced and α,β-methylene ATP-induced cAMP production but had no effect on adenosine-induced cAMP production. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed the presence of P2Y 11 receptor as well as A 2A and A 2B receptor mRNA in chronic lymphocytic leukemia lymphocytes. However, A 2B receptors would appear to be relatively ineffective because the A 2A selective agonist, CGS-21680 exhibited comparable efficacy to NECA. Furthermore, the A 2A-selective antagonist 8-(3-chlorostyryl)-caffeine (CSC) right-shifted the concentration–response curve for NECA. Taken together, the data indicate that ATP induces cAMP accumulation via the activation of P2Y 11 receptors whereas adenosine induces cAMP accumulation via the activation of A 2A receptors. Coordinate activation of P2Y 11 and A 2A receptors may influence the developmental fate of normal B-lymphocytes.