M. Laurent et al., KINETIC MODELING OF THE NITRIC-OXIDE GRADIENT GENERATED IN-VITRO BY ADHERENT CELLS EXPRESSING INDUCIBLE NITRIC-OXIDE SYNTHASE, Biochemical journal, 314, 1996, pp. 109-113
Inducible nitric oxide (NO) synthase produces a long-lasting NO flux w
hich can exert cytotoxic effects on target cells. A prerequisite for t
he understanding of the molecular basis of NO action is quantitative d
ata on the availability of this small neutral radical molecule at both
the spatial and temporal levels. The limits of NO availability depend
on the respective rates of NO production, diffusion and autoxidation
by molecular oxygen. Kinetic modelling of these processes has been per
formed for a widely used experimental system consisting of a monolayer
of adherent cells cultured in vitro for hours in unstirred culture me
dium. It appears that: (i) the maximal NO concentration in the culture
is in the immediate vicinity of the monolayer, where target cells wil
l sediment; (ii) the steady-state NO concentration in this area is low
er than 4 to 5 mu M; and (iii) measurements of nitrite/nitrate or citr
ulline accumulation in the bulk cell medium culture during a given tim
e period significantly underestimate (by a factor of up to 3 to 4) the
true rate of NO synthesis at the level of the producer cell. This rat
e can be, nevertheless, easily estimated from the rate of production o
f the stable NO synthase products.