ABSTRACT
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.
Subject(s)
Excitatory Amino Acid Agonists/pharmacology , N-Methylaspartate/pharmacology , Nitric Oxide/biosynthesis , Polyamines/analysis , Retina/chemistry , Animals , Arginine/metabolism , Cells, Cultured , Chick Embryo , Citrulline/biosynthesis , Cyclic GMP/metabolism , Eflornithine/pharmacology , Enzyme Inhibitors/pharmacology , Glycine/pharmacology , NADPH Dehydrogenase/antagonists & inhibitors , NADPH Dehydrogenase/metabolism , Nitric Oxide Synthase/metabolism , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Receptors, N-Methyl-D-Aspartate/metabolism , Retina/cytology , Retina/enzymology , Spermidine/pharmacologyABSTRACT
Beta-endorphin (beta-end) was investigated for its ability to influence sequential metabolic events that accompany the movements of T-lymphocytes into the cell cycle. When cultured lymphocytes are exposed to this endogenous opioid peptide an increase in polyamine transport across cell membrane is observed. This membrane modification is an early cell cycle event, whose enhancement leads to the intracellular polyamine accumulation. It is shown that beta-end is able to enhance spermidine transport and that the exposition of cells to this peptide is perceived as an apoptotic signal. The possible relationship between induction of apoptotic death and enhancement of polyamine uptake is discussed.
Subject(s)
Cell Cycle/drug effects , Lymphocytes/cytology , Lymphocytes/drug effects , beta-Endorphin/pharmacology , Apoptosis/drug effects , Cell Death/drug effects , Cell Division/drug effects , Cells, Cultured , DNA/biosynthesis , Flow Cytometry , G1 Phase/drug effects , Humans , Interphase/drug effects , Intracellular Fluid/metabolism , Lymphocyte Activation/drug effects , Lymphocytes/metabolism , Polyamines/metabolism , Protein Biosynthesis , S Phase/drug effectsABSTRACT
Opioid peptides, such as beta-endorphin (beta-end), are capable of modulating in vitro proliferative response of lymphocytes. We attempted to determine the role of extracellular polyamines in the regulation of immune responses to opioid peptides by measuring the extent of polyamine uptake as adaptional response to cell activation. beta-end dose-dependently enhanced the incorporation of radioactive spermidine and spermine. When the cells were depleted of spermidine, with addition of specific inhibitors of both biosynthesis and interconversion pathway, a large increase in the incorporation of radioactive spermidine was observed. This effect appeares to be specific for beta-end, although a non-opiate-specific receptor could be involved, since beta-end-enhanced incorporation of radioactive spermidine is not blocked by naloxone. We conclude that the enhancement of polyamine incorporation may be considered as an integral component of lymphocyte activation by beta-end.
