ADP-sensitive purinoceptors induce steroidogenesis via adenylyl cyclase activation in bovine adrenocortical fasciculata cells

1. The role of P2Y receptors in the production of cAMP and the activation of protein kinase A (PKA) was studied with respect to the regulation of the steroidogenesis in primary cultures of bovine adrenocortical fasciculata cells (BAFCs). 2. ADP and ATP stimulated cAMP production with EC₅₀ values of 23.7±6.8 μM and 40.1±5.5 μM, respectively. In contrast, the EC₅₀ of BzATP for cAMP production was 153.0±37.4 μM. Adenosine and AMP (0.1-1000 μM) were much less effective than ADP and ATP. 2MeSADP and UTP did not exert detectable effects. ADP (10 and 100 μM) significantly stimulated steroidogenesis; the process was blocked by an adenylyl cyclase inhibitor SQ22536 (100 μM) but not by the P2Y₁ receptor antagonist MRS2179 (100 μM). 3. Real-time imaging of the PKA activity with the dye ARII, which became less fluorescent upon phosphorylation, revealed that ADP (100 μM) immediately activated PKA. These effects could be mimicked by forskolin (100 μM) and were blocked by the PKA inhibitor H89 (50 μM). UTP (100 μM) did not activate PKA. 4. The cytoplasm harvested from morphologically and electrophysiologically identified single BAFCs contained mRNA for P2Y₂ but not for P2Y₁, P2Y₄, P2Y₁₁ or P2Y₁₂ receptors, as confirmed by single-cell RT-PCR amplification (50 cycles). 5. These results suggest an expression of an ADP-sensitive G_s-coupled purinoceptor in BAFCs. We propose that this not yet described type of P2Y receptor might mediate the extracellular purine-activated steroidogenesis via cAMP/PKA-mediated pathways, independently from the pathways involving InsP₃ production and consequent intracellular Ca²⁺ increase.