guanosine-monophosphate and 2-amino-7-phosphonoheptanoic-acid

AMPA (EC50 = 1.0 x 10(-6) M) and NMDA (EC50 = 1.3 x 10(-4) M) trigger 45Ca2+ influx in 13-day chick embryonic retinal explants. This agonist-driven cationic flux is specifically inhibited by typical competitive antagonists, such as 6,7-dinitroquinoxaline-2,3-dione (DNQX) and 2-amino-7-phosphonoheptanoate (AP7), respectively. Guanine nucleotides, with different degrees of phosphorylation, namely 5'-GMP, guanosine 5'-O-(2-thiodiphosphate) (GDPbetaS), guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) and 5'-guanylyl-imidodiphosphate (GppNHp), are also efficient blockers of 45Ca2+ influx. These results confirm the antagonistic behavior of guanine nucleotides towards ionotropic glutamate receptors and suggest a convenient experimental approach for screening of novel agonists and antagonists.

Topics: 2-Amino-5-phosphonovalerate; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Biological Transport; Calcium; Calcium Radioisotopes; Chick Embryo; Excitatory Amino Acid Antagonists; Guanine Nucleotides; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Monophosphate; N-Methylaspartate; Organ Culture Techniques; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Retina; Thionucleotides