Search

JC-1, a cationic fluorescent dye when added to living cells, is known to be localized exclusively in mitochondria, particularly in good physiological conditions characterized by sufficient mitochondrial membrane potential (ΔΨ). The accumulation of JC-1 in these organelles leads to the formation J-aggregates (with a specific red fluorescence emission maximum at 590 nm), which is in addition to the typical green fluorescence of J-monomers (emission maximum of ∼529 nm). The lack of mitochondrial ΔΨ leads to the depression of JC-1 mitochondrial accumulation and a decrease in J-aggregate formation. Therefore, the ratio between the red and green fluorescence of cells loaded with JC-1 is often used for the detection of the mitochondrial membrane potential. However, JC-1 represents a suitable substrate of the multidrug transporter P-glycoprotein (P-gp). Therefore, the depression of the JC-1 content in intracellular space and particularly in the mitochondria to a level that is inefficient for J-aggregate formation could be expected in P-gp-positive cells. In the current paper, we proved this behavior on parental P-gp-negative L1210 (S) cells and their P-gp-positive variants obtained by either selection with vincristine (R) or transfection with the human gene encoding P-gp (T). P-glycoprotein inhibitors cyclosporine A and verapamil fail to restore JC-1 loading of the R and T cells to an extent similar to that observed in S cells. In contrast, the noncompetitive high affinity P-gp inhibitor tariquidar fully restored JC-1 accumulation and the presence of the typical red fluorescence of J-aggregates. In the presence of tariquidar, measurement of the JC-1 fluorescence revealed similar levels of mitochondrial membrane potential in P-gp-negative (S) and P-gp-positive cells (R and T).

Haloperidol is an antipsychotic agent that primarily acts as an antagonist of D2 dopamine receptors. Besides other receptor systems, it targets sigma 1 receptors (σ1Rs) and inositol 1,4,5-trisphosphate receptors (IP 3 Rs). Aim of this work was to investigate possible changes in IP 3 Rs and σ1Rs resulting from haloperidol treatment and to propose physiological consequences in differentiated NG-108 cells, i.e., effect on cellular plasticity. Haloperidol treatment resulted in up-regulation of both type 1 IP 3 Rs (IP 3 R1s) and σ1Rs at mRNA and protein levels. Haloperidol treatment did not alter expression of other types of IP 3 Rs. Calcium release from endoplasmic reticulum (ER) mediated by increased amount of IP 3 R1s elevated cytosolic calcium and generated ER stress. IP 3 R1s were bound to σ1Rs, and translocation of this complex from ER to nucleus occurred in the group of cells treated with haloperidol, which was followed by increased nuclear calcium levels. Haloperidol-induced changes in cytosolic, reticular, and nuclear calcium levels were similar when specific σ1 blocker -BD 1047- was used. Changes in calcium levels in nucleus, ER, and cytoplasm might be responsible for alterations in cellular plasticity, because length of neurites increased and number of neurites decreased in haloperidol-treated differentiated NG-108 cells.