Intracellular polyamine levels are involved in NMDA-evoked nitric oxide production in chick retina cells

The NMDA-sensitive glutamate receptor complex can be modulated by numerous drugs and endogenous substances such as polyamines. We studied the pathway of arginine/nitric oxide/cyclic GMP in cultured chick retina cells through NMDA receptor activation, seen as a function of both differentiation stages of culture and intracellular polyamine levels. In our experimental conditions, the nitric oxide synthase activity was stimulated by NMDA from three to four times between embryonic day (E) 8 plus 5 days in vitro (C) and E8C7. The NMDA response was blocked by MK-801 (10 microM) by >60% at stage E8C5. During culture differentiation, the NMDA-induced increase in nitric oxide synthase activity at the E8C5 stage was blocked by preliminary incubation (24 h) of the cells with alpha-difluoromethylornithine, the inhibitor of polyamine biosynthesis. This effect was assessed by a reduction of NMDA-evoked cyclic GMP formation in polyamine-depleted retina cells. Thus, intracellular polyamine levels are involved in NMDA-evoked nitric oxide production. Our results indicate that (a) the developmental pattern of polyamine levels can be associated with the modulation of NMDA-evoked events and (b) the NMDA-mediated effects have been reduced in alpha-difluoromethylornithine-treated cell cultures. These observations provide evidence for a physiological interaction between polyamines and NMDA-sensitive glutamate receptors during differentiation stages of cultured chick retina cells.