Temperature dependence of active K+ transport in cation dimorphic sheep erythrocytes

Selective modulation of membrane sphingomyelin fatty acid turnover by nigericin. A study in the rat reticulocyte

Exposure of rat reticulocytes to Nigericin produced a selective modulation of fatty acid incorporation into sphingomyelin (SM) of the cell membrane, via changes in SM acylation kinetics. At physiological fatty acid concentration, Nigericin accelerated 8-fold SM acylation by decreasing the apparent K(m) for oleate from 14.7 microM to 2.0 microM. The response was diminished in high K(+)-containing media, suggesting an effect of Nigericin as K+ transporter. This constitutes a novel piece of evidence for the important role of ions in SM metabolism.

Dynamics of cell membrane permeability changes at supraphysiological temperatures

A quantitative fluorescent microscopy system was developed to characterize, in real time, the effects of supraphysiological temperatures between 37 degrees and 70 degrees C on the plasma membrane of mouse 3T3 fibroblasts and isolated rat skeletal muscle cells. Membrane permeability was assessed by monitoring the leakage as a function of time of the fluorescent membrane integrity probe calcein. The kinetics of dye leakage increased with increasing temperature in both the 3T3 fibroblasts and the skeletal muscle cells. Analytical solutions derived from a two-compartment transport model showed that, for both cell types, a time-dependent permeability assumption provided a statistically better fit of the model predictions to the data than a constant permeability assumption. This finding suggests that the plasma membrane integrity is continuously being compromised while cells are subjected to supraphysiological temperatures.

Effects of hyperthermia on avian red blood cells

Our primary goal was to develop a model for studying the effects of heat on terminally differentiated cells. Using nucleated chicken red blood cells (RBC) as the model, heat dose-response and thermotolerance were investigated. A new haemolytic assay was developed to score them. Heating chicken RBC for as long as 3 h at 51.5 degrees C resulted in only small amounts of haemolysis immediately after heating. When haemolysis was scored 1-2 days after heating, heat-induced haemolysis increased with heating temperature and duration. Heat shock of 30-90 min at 42.6 degrees C just before heat challenge of 40 min at 51.5 degrees C, or heat shock of 15 min at 43.1 degrees C with incubation of 0-2 h at 35-37 degrees C prior to the same heat challenge induced thermotolerance, but the levels of heat resistance achieved were different. Similar experiments were performed using potassium leakage as the endpoint. Potassium leakage was measurable immediately after heating, and it increased with heating duration, but there was no correlation between potassium leakage and haemolysis. Potassium leakage was not a suitable criterion for measuring thermotolerance.

Membrane effects of ionizing radiation and hyperthermia

Results of numerous studies demonstrate that membranes are important sites of cell damage by both ionizing radiation and hyperthermia. Modification of membrane properties (mainly lipid fluidity) affects the cellular responses to radiation and hyperthermia but former concepts that membrane rigidification sensitizes cells to radiation while membrane fluidization potentiates hyperthermic damage have now been seriously challenged. It seems that the effects of membrane fluidity on cell responses to hyperthermia and radiation are due to an indirect influence on functional membrane proteins. The major role of lipid peroxidation in radiation damage to membranes has also been questioned. The existing evidence makes it unlikely that the interaction between radiation and hyperthermia is determined by the action of both agents on the same membrane components.

Potassium-induced reverse transformation of cells infected with a temperature-sensitive transformation mutant virus

High potassium concentrations altered the morphology and the ability to grow in soft agar in 6m2 cells, a clone of rat kidney cells infected with a temperature-sensitive mutant of Moloney sarcoma virus. Approximately 60% of cells exhibited normal morphology in the presence of 94.8 mM potassium in isotonic medium at the temperature permissive for transformation, whereas 100% were normal at 72 mM potassium in hypertonic media. A significant reduction of growth in soft agar was also induced with these conditions. However, the synthesis ratio of virus-specified transforming protein to marker viral protein was not altered. Na+K+-ATPase might play a role in this reverse-transformation process.

Active ion transport in the renal proximal tubule. I. Transport and metabolic studies

Various aspects of the interrelationship between ion transport and cellular metabolism were investigated using a suspension of rabbit cortical tubules that were mainly proximal in nature. Using the intact tubules, the compartmentation of K within the renal cell was studied by performing 42K uptake studies. The oxygen consumption (QO2) of the tubules was measured under similar conditions, as well as when the Na pump was stimulated by increasing Na+ entry with nystatin. In addition, the state 3 rate of respiration was measured when the mitochondria of digitonin-permeabilized tubules were stimulated by ADP. At 37 and 25 degrees C, a single-compartmental uptake of 42K was observed, which suggests that extracellular K+ communicates with a single compartment within the renal cell. Between 37 and 15 degrees C, the ouabain-sensitive QO2 and the initial 42K uptake rate were parallel in an Arrhenius-type plot, which indicated that active ion transport and oxidative phosphorylation remain tightly coupled within this temperature range. At all temperatures between 37 and 15 degrees C, nystatin stimulated the QO2, which demonstrates that the entry of Na+ into the renal cells was rate limiting for active Na+ transport throughout this temperature range. Between 37 and 20 degrees C, the nystatin-stimulated QO2 was nearly equal to the state 3 rate of respiration, which suggests that active ion transport may be limited by ATP availability under these conditions. At 15 degrees C, nystatin addition stimulated the QO2 well below the state 3 respiratory rate.

Comparative study of the transition temperature of calf and adult cattle erythrocytes

In our study we have compared the temperature dependence of osmotic fragility in calf and adult cattle erythrocytes. The temperature dependence of osmotic fragility has revealed inflections in calf red cells generally at 20 degrees C (293 K), in adult cattle red cells at about 30 degrees C (303 K). One possible explanation for the lower transition temperature of calf erythrocytes is that the microviscosity of the protein-lipid boundary might be considerably less in the membrane of the calf cell than in the adult cell.