These results indicate that the drug interacts with the mitochondrial membrane and that the interaction is more likely to occur in its external portion. Mitochondria perform a variety of biochemical processes, but their main function is to produce the majority (>90%) of cellular ATP via oxidative phosphorylation, which is dependent upon a proton electrochemical gradient generated by respiration and maintained by the impermeability of the inner mitochondrial membrane to protons (Kehrer and Lund, 1994;

Pessayre et al., 1999). However, if the mitochondrial membrane is rendered permeable to protons, the membrane potential dissipates, increasing the respiratory rate. Under this condition (uncoupling), the organelle is no longer capable of sustaining ATP GSK458 purchase synthesis (Mitchell, 1961; Nicholls, 1982). Juliprosopine induced an increase in the state-4 respiration,

both in mitochondria energized with malate and pyruvate or with succinate. This effect was accompanied by the dissipation of the membrane potential with a concomitant reduction in ATP synthesis by Epacadostat molecular weight the organelle. Furthermore, the compound also caused a stimulation of oxygen uptake in the mitochondria in the presence of oligomycin. Taken together, these results indicate that juliprosopine acts as an uncoupler of oxidative phosphorylation, transforming the mitochondria from an essential powerhouse of the cell Beta adrenergic receptor kinase into a molecular furnace, efficiently wasting the metabolic energy of substrates (Wallace and Starkov, 2000). This change results in a reduction in ATP synthesis, an important event that may cause cell death (Nicotera et al., 1998; Wallace and Starkov, 2000; Szewczyk and Wojtczak, 2002). The interference caused by juliprosopine in the mitochondrial bioenergetic process may be responsible for the results obtained by Silva et al. (2007), who studied the effects of the total alkaloid extract and alkaloid fractions of the plant P. juliflora in a primary

astrocyte culture. They observed that exposure to those compounds caused numerous cytotoxic effects, such as a decrease in MTT reduction, release of the enzyme lactate dehydrogenase (LDH) and morphological changes related to cell death. One class of uncouplers is the protonophorics, such as 2,4-dinitrophenol and CCCP (m-chlorophenylhydrazone), which are weak acids that increase the proton conductance of the inner mitochondrial membrane (Mitchell and Moyle, 1967; Terada, 1990; Skulachev, 1998; Wallace and Starkov, 2000). These compounds can trigger the process of mitochondrial swelling in hyposmotic potassium acetate medium (Nicholls, 1982). Even at the highest concentration tested in this study (25 μM), juliprosopine did not have the capacity to induce swelling, thereby rejecting the hypothesis that it has protonophoric activity.