1021-4437/05/5202- © 2005
Russian Journal of Plant Physiology, Vol. 52, No. 2, 2005, pp. 182–188. Translated from Fiziologiya Rastenii, Vol. 52, No. 2, 2005, pp. 209–215.
Original Russian Text Copyright © 2005 by Shugaev, Andreev, Vyskrebentseva.
It is well known that animal mitochondria are
enriched in potassium ions  and that
is the main
osmotically active component of the mitochondrial
matrix. This cation is involved in the regulation of mito-
chondrial volume and of enzyme activities associated
with these organelles . Since
is signiﬁcant for
mitochondrial functioning, the mechanisms of K
transport attract close attention for a long time already
It is well established to date that the K
across the inner membrane in mitochondria of animal
cells is mediated by two transport systems, namely, a
antiporter and an ATP-sensitive
whose properties are partly characterized [6–10]. It is
thought that a concerted operation of these
porters ensures cyclic transport of potassium across
the inner membrane and represents the principal
mechanism in the control of matrix volume in animal
mitochondria [7, 10].
-transporting systems may
function in the inner membrane of plant mitochondria,
although available information is quite scarce. For
example, the presence of electroneutral
porter in plant mitochondria was demonstrated .
Recent data indicate the presence of
channel in the inner membrane of mitochondria iso-
lated from several plant species [12, 13]. These data
provide ground to believe that such a channel is a ubiq-
uitous component of plant mitochondria. However,
many aspects of operation, regulation, and possible
functional role of this transport system remain unclear.
Nevertheless, the research in this direction is of consid-
erable interest and may contribute to our knowledge of
plant mitochondria functioning.
Our previous experiments with mitochondria from
sugar beet taproots showed that kinetic characteristics
of active swelling of these organelles in
buffer solutions ﬁt into a model of the selective electro-
uniporter operating in the inner membrane .
Functional Identification of ATP-Sensitive K
in Mitochondria from Sugar Beet Taproot
A. G. Shugaev, I. M. Andreev, and E. I. Vyskrebentseva
Timiryazev Institute of Plant Physiology, Russian Academy of Sciences,
Botanicheskaya ul. 35, Moscow, 127276 Russia;
fax: 7 (095) 977-8018; e-mail: firstname.lastname@example.org
Received February 10, 2004
—Mitochondria isolated from sugar beet (
L.) taproot were shown to swell spontane-
ously after the transfer from a sucrose-containing isolation medium to isoosmotic potassium chloride solutions.
The kinetics of this process was strongly retarded after the replacement of potassium with sodium in the incu-
bation medium and was substantially stimulated by the electron-transport chain activity and valinomycin. At
neutral pH of the incubation medium, the rate of K
-dependent swelling of mitochondria decreased by 30–50%
after adding 1 mM ATP but was insensitive to other nucleotides (GTP, UTP, and CTP). In the medium acidiﬁed
to pH 6.0, the addition of ATP caused shrinkage of mitochondria that had been swollen in the KCl medium. In
the absence of this nucleotide, the kinetics of K
-dependent swelling of mitochondria was considerably decel-
erated upon the acidiﬁcation of the incubation medium. The effects of ATP were independent of the presence
or absence of oligomycin and atractyloside. However, the ATP-dependent shrinkage of mitochondria was inhib-
ited in the presence of quinine, and this agent also inhibited K
-dependent swelling of organelles in potassium
acetate solutions. The presence of K
ions in the incubation medium caused a rapid dissipation of the mitochon-
drial membrane potential (
) that was generated during succinate oxidation. The addition of ATP to the reac-
tion medium resulted in the oligomycin-insensitive restoration of
. The results are regarded as evidence that
the membrane of taproot mitochondria is endowed with functionally active ATP-sensitive K
system is likely to represent a K
channel that catalyzes the electrogenic transfer of potassium ions to the mito-
chondrial matrix. It is supposed that the membrane of taproot mitochondria also contains a quinine-sensitive
antiporter that catalyzes the efﬂux of potassium from the matrix or, on the contrary, the accumulation of
in the presence of potassium acetate.
Key words: Beta vulgaris - taproot - mitochondria - potassium transport
: FCCP—carbonyl cyanide (
phenylhydrazone; ROS—reactive oxygen species;
potential difference at the inner membrane of mitochondria.