Zinc protoporphyrin IX suppresses nitric oxide production through a loss of L-arginine in rat cerebellar slices.
Zinc protoporphyrin IX (ZnPP) inhibits production of carbon monoxide (CO) but not nitric oxide (NO) synthase activity in vitro, therefore, it has been used to discriminate the effects of these activators of cyclic GMP production. However, intracellular enzyme activity is supported by endogenous substrates and cofactors, therefore, in vitro experiments with an optimal supply of these substances do not necessarily represent the intracellular circumstances. The present study was conducted to examine whether ZnPP affects NO production in rat cerebellar slices. Incubation with 1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD) increased the conversion of [3H]-L-arginine into [3H]-citrulline in the slices. ZnPP at I microM, not only suppressed the ACPD-dependent production of [3H]-citrulline but also reduced the basal [3H]-citrulline level, accumulation of [3H]-L-arginine and ATP content in the slices, but ZnPP at 1 microM did not affect the catalytic activity of partially purified NO synthases in vitro. In contrast, a selective inhibitor of NO synthase, N omega(-)nitro-L-arginine, inhibited ACPD-dependent [3H]-citrulline production without affecting the basal [3H]-citrulline level or [3H]-L-arginine accumulation. These results indicate that ZnPP suppresses No production through a loss of its precursor, even at concentrations exhibiting no inhibition of the catalytic activity of NO synthase. It is concluded that ACPD activates NO synthase in the slice and that ZnPP cannot discriminate the roles of CO from NO in cyclic GMP production in brain slices.
Okada
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Laboratory for Synaptic Functions, Institute of Physical and Chemical Research, (RIKEN), Saitama, Japan.
D000818:Animals; D001120:Arginine / Q000378:metabolism*; D002531:Cerebellum / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D011524:Protoporphyrins / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D004791:Enzyme Inhibitors; D011524:Protoporphyrins; C017803:zinc protoporphyrin; D009569:Nitric Oxide; D001120:Arginine