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G Fiskum

Publications and source records attributed to G Fiskum.

84 records · Page 5Linked to original sources
PubMed1983

Involvement of mitochondria in ischemic cell injury and in regulation of intracellular calcium.

Ischemia causes a pathological drop in the cellular energy state due to inhibition of mitochondrial oxidative phosphorylation. The reversibility of this condition depends on the damage to mitochondrial membrane-linked activities during the period of ischemia or during reoxygenation of the tissue. It is likely that the ischemia-induced damage is due to a combination of factors including an increase in the cytosolic free Ca2+ concentration, a triggering of phospholipase and protease activities, an increase in cellular free fatty acids, and a decrease in pH. Mitochondrial damage that occurs during reperfusion is probably a consequence of excessive mitochondrial Ca2+ accumulation under adverse intracellular conditions. Mitochondria normally have an extremely high capacity for sequestering and buffering cytosolic Ca2+. However, during postischemic reperfusion these processes are inhibited due to existing conditions that potentiate Ca2+ uptake-induced irreversible mitochondrial damage.

Adenosine Triphosphate↗
PubMed1980

Regulation of free Ca2+ by liver mitochondria and endoplasmic reticulum.

Electrode measurements were made of the free Ca2+ concentration maintained by suspensions of isolated rat liver mitochondria and microsomes, as well as by hepatocytes whose plasma membranes had been made permeable by treatment with digitonin. When the KCl, ATP, Mg2+, and phosphate concentrations were made similar to that of cytosol, the steady state free Ca2+ concentration in the presence of respiring mitochondria alone was about 0.5 microM. The additional presence of rat liver microsomes resulted in a steady state level of close to 0.2 microM, which was maintaied for greater than 1 h at 25 degrees C. This concentration of Ca2+ was also maintained by suspensions of hepatocytes permeabilized by digitonin and thus may approximate the actual cytosolic free Ca2+ concentration in vivo. The "set point" for free Ca2+ homeostasis in these systems is determined by mitochondrial Ca2+ influx-efflux cycling, which is dependent on the level of intramitochondrial Ca2+ and can be adjusted by sequestration of Ca2+ in microsomes.

Animals↗
PubMed1980

The cytoskeleton of digitonin-treated rat hepatocytes.

Treatment of isolated rat hepatocptes with low concentrations of digitonin increases the permeability of the plsma membrane to cytosolic proteins without causing release of organelles such as mitochondria into the surrounding medium. Electron microscopy showed that treatment of the cells with increasing concentations of digitonin results in a progressive loss in the continuity of the plasma membrane, while most other aspects of cellular morphology remain normal. Depletion of background staining material from the cytosol by digitonin treatment of the cells greatly enhances the visualization of the cytoskeleton. The use of this technique, together with immunofluorescent light microscopy, has verified the presence of an actin-containing filamentous network at the hepatocyte cortex as well as intermediate filaments distributed throughout the cell. Digitonin is thus useful both for selectively permeabilizing the plasma membrane and for intensifying the appearance of intracellular structures such as microfilaments that are normally difficult to observe in cells such as hepatocytes.

Actins↗
PubMed1979

Regulated release of Ca2+ from respiring mitochondria by Ca2+/2H+ antiport.

Simultaneous measurements of oxygen consumption and transmembrane transport of Ca2+, H+, and phosphate show that the efflux of Ca2+ from respiring tightly coupled rat liver mitochondria takes place by an electroneutral Ca2+/2H+ antiport process that is ruthenium red-insensitive and that is regulated by the oxidation-reduction state of the mitochondrial pyridine nucleotides. When mitochondrial pyridine nucleotides are kept in a reduced steady state, the efflux of Ca2+ is inhibited; when they are in an oxidized state, Ca2+ efflux is activated. These processes were demonstrated by allowing phosphate-depleted mitochondria respiring on succinate in the presence of rotenone to take up Ca2+ from the medium. Upon subsequent addition of ruthenium red to block Ca2+ transport via the electrophoretic influx pathway, and acetoacetate, to bring mitochondrial pyridine nucleotides into the oxidized state, Ca2+ efflux and H+ influx ensued. The observed H+ influx/Ca2+ efflux ratio was close to the value 2.0 predicted for the operation of an electrically neutral Ca2+/2H+ antiport process.

Animals↗
PubMedDate not supplied

Global cerebral ischemia and reperfusion alters NMDA receptor binding in canine brain.

We employed a canine model to test whether binding to the N-methyl-D-aspartate (NMDA) class of glutamate receptor channels is altered by global cerebral ischemia and/or reperfusion. Ischemia was induced by 10-min cardiac arrest, followed by restoration of spontaneous circulation for periods of 0, 0.5, 2, 4, and 24 h. In vitro autoradiography was performed on frozen brain sections with three radioligands: [3H]glutamate (under conditions to label the NMDA site), [3H]glycine, and [3H]MK-801. Modest decreases in [3H]glutamate and [3H]MK-801 binding were seen in several regions of hippocampus, and parietal and temporal cortex at early times after reperfusion, with values returning toward control by 24 h. In the striatum, a different pattern was seen: [3H]glutamate and [3H]MK-801 binding increased 50-200% at 0.5-4 h after the start of reperfusion, returning toward control levels by 24 h. These increases correlate with findings of increased sensitivity to NMDA-stimulated release of dopamine from striatal tissue in the same model (Werling et al., 1993), and suggest that changes in tissue receptors may contribute to the selective vulnerability to ischemic damage during the first hours following reperfusion.

Animals↗
PubMedDate not supplied

Substance P analogues function as bombesin receptor antagonists and inhibit small cell lung cancer clonal growth.

Human small cell lung cancer (SCLC) produces and secretes BN/GRP (bombesin/gastrin releasing peptide). Because BN stimulates the growth of SCLC cells and these cells have receptors for BN-like peptides, it is important to define agents which disrupt this self-promoting autocrine growth cycle. Here, substance P analogues were evaluated as BN receptor antagonists using SCLC cell lines. (D-Arg1, D-Pro2, D-Trp7.9, Leu11) substance P [(APTTL)SP] was one of the more potent analogues tested in inhibiting BN-like peptide receptor binding with an IC50 value of 1 microM. Micromolar concentrations of (APTTL)SP antagonized BN receptor mediated elevation of cytosolic Ca2+ levels and decreased the colony formation in soft agarose. These data suggest that SP analogues function as SCLC BN receptor antagonists and may be useful in disrupting the autocrine growth function of BN-like peptides.

Bombesin↗
PubMedDate not supplied

Neurotensin elevates cytosolic calcium in small cell lung cancer cells.

The ability of neurotensin (NT) to elevate cytosolic Ca2+ in small cell lung cancer (SCLC) cells was investigated using the fluorescent Ca2+ indicator Fura 2-AM. Using SCLC cell line NCI-H345, NT elevated cytosolic Ca2+ levels in a concentration-dependent manner. Using a 10 nM dose, NT and C-terminal fragments such as NT(8-13) but not N-terminal fragments such as NT(1-8) elevated the cytosolic Ca2+ levels. Because EGTA (5 mM) did not affect the NT response, NT may cause release of Ca2+ from intracellular stores. These data indicate that SCLC NT receptors may use Ca2+ as a second messenger.

Calcium↗
PubMedDate not supplied

Lack of a neuroprotective effect from N-acetylcysteine after cardiac arrest and resuscitation in a canine model.

OBJECTIVE: Oxygen free radicals cause brain injury following resuscitation from cardiac arrest. In preclinical trials, some free radical scavenging drugs reduce oxidative neuronal damage after ischemia and reperfusion, but these drugs are generally not yet available for clinical testing or use. N-Acetylcysteine (NAC), a commonly used antidote in acetaminophen poisoning, is also a potent free radical scavenger that can ameliorate oxidative injury following ischemia and reperfusion in neuronal cell culture. We hypothesized that treatment with NAC would improve neurological outcome after cardiac arrest and resuscitation. METHODS: In 16 adult female beagles, 10 min of ventricular fibrillation was followed by 3 min of open-chest CPR, and defibrillation. Immediately following return of spontaneous circulation, animals randomly received either 150 mg/kg NAC (3% solution) (n = 8) or an equivalent volume of normal saline (n = 8). Twenty-three hours later, neurological deficit was scored (0 = normal, 100 = brain death). RESULTS: All animals were successfully resuscitated, and there were no apparent adverse effects to the administration of NAC in post resuscitative animals. There was, however, no significant difference in neurological deficit in the animals receiving NAC (40 +/- 12.9, mean +/- SD) compared to control animals (44 +/- 6.5, P = 0.73). CONCLUSION: No neuroprotective effect was found from the administration of NAC at currently used clinical dosages, to dogs subjected to 10 min of global cerebral ischemia from cardiac arrest and resuscitation.

Acetylcysteine↗