The potassium level in mitochondria is regulated by a K1ATP
channel, recently identi®ed, whose opening can be induced by
cyclosporin A. In addition, plant mitochondria have an electroneutral
H1/K1 exchanger and a putative chloride channel which, acting
in concert with the K1ATP channel, can accomplish a K1 cycling.
In this work, we present evidence on the modulation of the K1ATP
channel of pea stem mitochondria by NO and H2O2, and on its
possible involvement in cytochrome c release. Pea stem mitochondria,
resuspended in a KCl medium (de-energized mitochondria),
underwent a swelling, as a consequence of K1 entry, that was
inhibited by ATP. This inhibition was partially restored by GTP
and diazoxide (K1 channel openers). In addition, glyburide and 5-
hydroxydecanoate (K1ATP channel blockers) induced an inhibition
of the GTP-stimulated swelling. Mitochondrial swelling was inhibited
by H2O2 (generated by glucose±glucose oxidase), but stimulated
by NO (released by potassium nitroprusside). The same results
were also obtained in succinate-energized mitochondria. When the
succinate-dependent electrical potential had reached a steady-state,
the addition of KCl induced a dissipation that was favoured by NO
and prevented by the NO scavenger, carboxy-PTIO. Hydrogen
peroxide prevented the stimulation by NO of the KCl-induced dissipation
of the electrical potential. The aperture of this channel was
linked to the partial rupture of the outer membrane, and the latter
effect led to a release of cytochrome c, but not of adenylate kinase.
These results show that the plant mitochondrial K1 channel resembles
that present in mammalian mitochondria. This channel can be
modulated by NO and H2O2 and is involved in the release of cytochrome
c, occurring during the manifestation of programmed cell
death. This conclusion is reinforced by the consideration that there
is no clear evidence for the presence of a permeability transition
pore in plant mitochondria which can perform this function.
