Proton selective substate of the mitochondrial permeability transition pore: regulation by the redox state of the electron transport chain

The permeability transition pore of rat liver mitochondria can be closed by chelating free Ca2+, with respect to the passage of large molecules such as mannitol and sucrose. However, an apparent H+-conducting substate remains open under these conditions, as indicated by the persistence of maximal O2 consumption rates and by the failure to recover a membrane potential. Agents which favor a closed pore, such as cyclosporin A, ADP, Mg2+, or bovine serum albumin, do not close the H+-conducting substate, but it closes spontaneously when respiration becomes limited by the availability of O2. Closure provoked by an O2 limitation requires free Mg2+ in the sub-micromolar concentration range and becomes less efficient with increasing time spent in the presence of free Ca2+. The H+-conducting substate is apparently regulated by the redox status of the electron transport chain, with a reduced form favoring closure. A physical association (or equivalence) between the pore and one of the respiratory chain complexes is supported. These characteristics suggest that the transition is irreversible in vivo, if it involves a small fraction of total mitochondria, and would lead to their elimination and/or replacement by the cell. The implications of this proposal are considered, as they relate to a possible role for the transition in cellular apoptosis and the elimination of mitochondria containing mutated DNA.     

Dental team''s role in tobacco cessation

In rat experiments new imidazoline derivatives caused a pain-relieving effect and inhibited a rise in arterial pressure in pain. Fluoride derivatives of imidazoline in doses of 1, 2, and 4 mg/kg induced long-term analgesia, had no effect on the background arterial blood pressure (AP), and significantly reduced its nociceptive pressor responses. The bromide derivatives of imidazoline showed no noticeable pain-relieving activity but reduced the nociceptive AP shifts. The background AP parameters did not change in this case. The prospects of directed chemical modification of imidazoline derivatives to obtain new analgesics capable of reducing the undesirable hemodynamic manifestations of pain are discussed.     

In situ levels of intracellular Ca2+ and pH in avian growth plate cartilage

Interactions with the extracellular matrix, accumulation of Ca2+, formation of matrix vesicles, and regulation of tissue pH by growth plate chondrocytes all appear to be vital to endochondral calcification. Thus, the activities of Ca2+ and H+ ions in these cells, while still embedded in their organic matrix, are of great interest. Using laser confocal imaging and sensitive Ca2+ (Indo 1) and pH (BCECF) probes, cellular Ca2+ and pH were analyzed in thin sections of freshly isolated cartilage. Mean values of cytosolic Ca2+ in cells from the various zones of the growth plate were quite similar, but levels in individual cells and subcellular compartments varied significantly. Ca2+ was elevated intensely near the periphery of cells in the zones of maturation and hypertrophy, and many Ca2+ rich particles were seen in the matrix near these cells. Levels of Ca2+ within the cells varied with time. In the proliferative region, cyclical increases and decreases in Ca2+ were seen, but there was little shedding of Ca2+ rich particles. However, after repeated Ca2+ cycling, in the zones of maturation and hypertrophy, Ca2+ rich particles were shed from the cell surface, forming what appeared to be matrix vesicles. Intracellular pH levels also varied significantly within the chondrocytes and between the cells and zones. Numerous focal elevations in pH (> 8.0) were seen in central regions of the maturing and early hypertrophic cells, with lower pH (6.5-7.2) near the cell periphery of the late hypertrophic and calcifying cells. This pattern of cytoplasmic alkalinization and subsequent acidification appears to contribute to loading of Ca2+ and Pi into matrix vesicles during their formation by the chondrocytes.     

Determination of zinc in fingernails by non-flame atomic absorption spectroscopy

The determination of Zn in fingernails directly using the graphite furnace presented certain difficulties due to the anomalous behavior of the analyte in the furnace. The appearance of two peaks which were due to Zn and not to any background interference was noted. The Zn value obtained by adding the area of these two peaks compared fairly well with Zn levels determined by wet ashing and subsequent determination either in the furnace or flame. Wet ashed samples gave only a single peak. It was possible to produce a model of the phenomenon with various Zn salts in a non aqueous matrix. Under these conditions ZnSO4 and ZnO gave a discretely different peak from ZnC12 or metallic Zn. Several tissues such as serum, whole blood, cuticle, and hair were examined for multiple peak formation. Direct determination of Zn in fingernails with the graphite furnace is possible for certain applications such as the determination of Zn levels of white spots in fingernails. For this purpose it is possible to use a sample size as small as 20 mug using the 2138 Zn line. This allows one to run several determinations on a single white spot. However, where sample size is not a limitation, wet ash digestion prior to determination in the furnace is probably the preferred procedure.