ACTION OF MODULATORS OF LARGE-CONDUCTANCE Ca <sup>2+</sup>-ACTIVATED K <sup>+</sup> CHANNELS ON RAT ASCITES HEPATOMA CELLS AND ISOLATED RAT LIVER MITOCHONDRIA TREATED BY Cd <sup>2+</sup>
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 Ca <sup>2+</sup>-dependent nonselective pore of the inner mitochondrial membrane. The role of other ion channels, in particular such selective potassium channels as Ca <sup>2+</sup>-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 Cd <sup>2+</sup> in the assay medium, namely of two its openers, NS1619 and NS004, and one blocker, paxilline. After 24 h-incubation of AS-30D cells with 10 μM of either NS1619 or NS004, 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 Cd <sup>2+</sup>-induced apoptosis of AS-30D cells. The same concentration of NS1619 and NS004 did not affect significantly respiration of AS-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 NS004, added at the same concentration to the KCl-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 Cd <sup>2+</sup>); 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 Cd <sup>2+</sup> 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 Cd <sup>2+</sup> 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 effect, paxilline did not influence the respiration of AS-30D cells and isolated rat liver mitochondria (both in the presence and absence of Cd <sup>2+</sup>) and did not decrease mitochondrial swelling observed in the presence of Cd <sup>2+</sup> and the BK(Ca) activators. Possible molecular mechanisms of action of the BK(Ca) modulators are discussed.