ATP-producing cell organelles, mitochondria, are the primary target for
heavy metals which are major
environmental pollutants and cause various pathological conditions and diseases. It has been established that the mechanism of
toxic action of
heavy metals, includes changes in the intracellular production of
reactive oxygen species and
mitochondrial dysfunction mediated by disturbances of the respiratory chain and by activation of Ca2+-dependent nonselective pore of the inner mitochondrial membrane. The role of other
ion channels, in particular such selective
potassium channels as Ca2+ activated large-conductance
potassium channels, BK(Ca), considered to be <<protective>> for a cell, is practically not investigated. In the present work on rat
ascites hepatoma AS-30D cells and isolated rat liver mitochondria we studied action of different BK(Ca) effectors in the absence and presence of Cd2+ in the assay medium, namely of two its openers, N51619 and N5004,and one blocker,
paxilline. After 24 h-incubation of AS-30D cells with 10 µM of either
NS 1619 or N5004, the number of apoptotic cells was found to increase compared with control. Besides, the presence of these BK(Ca) openers in the media produced an additive effect on Cd2+-induced apoptosis of AS-30D cells. The same concentration of N51619 and N5004 did not affect significantly respiration ofAS-30D cells after 3, 24 and 48 h of incubation but produced a substantial increase in intracellular production of
reactive oxygen species after 3 h of the treatment. In experiments on isolated rat liver mitochondria
NS1619 and N5004, added at the same concentration to the KCI-containing medium, had no effect on the respiratory rate at state 3 by Chance and on the maximally uncoupled respiration rate (both in the presence and absence of Cd2+); at the same time they induced a weak uncoupling action by accelerating the basal respiration and the resting state respiration (at state 4 by Chance) as well as they enlarged the high-amplitude mitochondrial swelling induced by Cd2+ in this medium. It was shown that
paxilline, at concentration of 1 µM, decreased the mortality of AS-30D cells after 3, 24 and 48 h of incubation in the presence of Cd2+ and enhanced intracellular production of
reactive oxygen species in control cells after 3 and 24 h of incubation. At concentration producing a long-term protective effeet,
paxilline did not influence the respiration of AS-30D cells and isolated rat liver mitochondria (both in the presence and absence of Cd2+) and did not decrease mitochondrial swelling observed in the presence of Cd2+ and the BK(Ca) activators. Possible molecular mechanisms of action of the BK(Ca) modulators are discussed.