Endogenous extracellular purine nucleotides redirect α2-adrenoceptor signaling

Many receptors coupled to inhibitory G(o)/G(i)-type G proteins often also produce stimulatory signals like Ca2+ mobilisation. When expressed in CHO cells the alpha(2)-adrenoceptor subtypes alpha(2A), alpha(2B) and alpha(2C) mobilised Ca2+, These responses were strongly reduced by the P-2y-purinoceptor antagonist suramin, A large proportion of the total pool of purine nucleotides was found extracellularly. Removal of extracellular nucleotides with apyrase or by constant perfusion had a similar effect as suramin. These treatments did not affect the adrenoceptor-mediated inhibition of cAMP production. This indicates that cells may be primed or their signaling pathways redirected towards Ca2+ mobilisation by 'autocrine' release of nucleotides. (C) 1998 Federation of European Biochemical Societies.