Characterization of "mini-nucleotides" as P2X receptor agonists in rat cardiomyocyte cultures. An integrated synthetic, biochemical, and theoretical study

The design and synthesis of "mini-nucleotides", based on a xanthine-alkyl p hosphate scaffold, are described. The physiological effects of the new comp ounds were evaluated in rat cardiac cell culture regarding Ca2+ elevation a nd contractility. The results indicate biochemical and physiological profil es similar to those of ATP, although at, higher concentrations. The biologi cal target molecules of these "mini-nucleotides" were identified by using s elective P2-R and A(1)-R antagonists and P2-R subtype selective agonists. O n the basis of these results and of experiments in Ca2+ free medium, in whi ch [Ca2+](i) elevation was not observed, we concluded that interaction of t he analogues is likely with P2X receptor subtypes, which causes Ca2+ influx . Theoretical calculations analyzing electronic effects within the series o f xanthine-alkyl phosphates were performed on reduced models at quantum mec hanical levels. Calculated dipole moment vectors, electrostatic potential m aps, and volume parameters suggest an explanation for the activity or inact ivity of the synthesized derivatives and predict a putative binding site en vironment for the active agonists. Xanthine-alkyl phosphate analogues prove d to be selective agents for activation of PBX-R subtypes, whereas ATP acti vated all P2-R subtypes in cardiac cells. Therefore, these analogues may se rve as prototypes of selective drugs aiming at cardiac disorders mediated t hrough P2X receptors.