ADENYLATED DINUCLEOTIDE BINDING TO THE ADENOSINE 5',5'''-P1,P4-TETRAPHOSPHATE MOUSE HEART RECEPTOR

We have demonstrated specific adenosine 5',5''' -P-1,P-4-tetraphosphat e (Ap(4)A) receptors at heart cell surfaces (1-3). Optimal Ap(4)A bind ing requires receptor activation (2, 4). Other investigators have demo nstrated that Ap(5)A and Ap(6)A act as vasopressors (5). We now compar e the binding of Ap(4)A, Ap(5)A and Ap(6)A on heart membranes to deter mine if all three ligands bind to the same receptor and their relative avidities. Anti-Ap(4)A receptor antibodies inhibit the binding of all three ligands. SDS-PAGE analysis of Ap(4)A, Ap(5)A and Ap(6)A cross-l inked to membranes reveals that all three are attached to a 30 kDa pep tide. The specific activity for binding to unactivated membranes is si milar for all three ligands. However, after receptor activation there is a 3.4x increase in Ap(4)A binding and a 32.5x decrease in the KD; v alues remain unchanged for Ap(5)A and Ap(6)A. These data indicate that Ap(4)A, Ap(5)A and Ap(6)A bind to the same receptor on cardiac membra nes but receptor activation enhances only Ap(4)A binding. (C) 1994 Aca demic Press, Inc.