Derivatives of the Triazoloquinazoline Adenosine Antagonist (CGS15943) (I) are Selective for the Human A3 Receptor Subtype.-The adenosine antagonist (I) binds to human A3 receptors with high affinity (Ki = 14 nM), while it lacks affinity at rat A3 receptors. A series of acylated derivatives, such as (III) and (V), are prepared for the provision of A3 subtype selectivity. A number of straight chain alkyl amides show that the optimal chain length occurs with derivative (IIIa), which has a Ki value of 7.7 nM at human A3 receptors and is 40-and 14-fold selective versus rat A1 and A2A receptors, respectively. (IIIb) displays Ki values of 680 and 273 nM at rat A1 and A2A receptors, resp., and 3.0 nM at human A3 receptors. ( V) is 470-fold selective to human A3 versus rat A1 receptors with Ki = 0.65 nM.
cAMP inhibits the contraction mechanism associated with intracellular Ca2+ mobilization as well as extracellular Ca2+ influx, while cGMP inhibits contraction by inhibiting the mechanism associated with extracellular Ca2+ influx.
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