Effect of cycloheximide on nonpermissive temperature killing in tsH1 mutant cells

1. 1.|We investigated the mechanism of cycloheximide-induced heat protection. We proposed a hypothesis to account for the mechanism [Lee and Dewey (1986) Radiat. Res. 106, 98–110].

2. 2.|Cycloheximide protects cells from hyperthermic killing by means of protecting thermolabile proteins from denaturation.

3. 3.|For this study, we have employed temperature-sensitive mutant tsH1 which contains a thermolabile leucyl-tRNA synthetase.

4. 4.|By 15 h of incubation at the nonpermissive temperature of 39.5 or 40°C, 40 or 93% of mutant cells respectively, were killed. In contrast, wild type SC cells did not lose viability after this same incubation.

5. 5.|Although killing of tsH1 by incubation at the nonpermissive temperatures was mainly due to denaturation of a thermolabile leucyl-tRNA synthetase, cycloheximide did not protect mutant cells from killing. However, tsH1 and SC cells exhibited similar sensitivities to killing at 43°C and above. Furthermore, cycloheximide protected both cell types from hyperthermic killing.

6. 6.|There was a 200- or 700-fold increase in survival after 2.5 h at 43°C by treatment with cycloheximide in tsH1 or SC cell type, respectively. Thus, the cellular target(s) for hyperthermic killing at this temperature apparently are similar in both types of cells.

7. 7.|The data indicate that the mechanism behind cycloheximide-induced heat protection is probably not the prevention of protein denaturation.

Thermohaemolysis of human erythrocytes in isotonic NaCl/sucrose media during transient heating

1. 1.|The hyperhermia induced haemolysis of cells and resealed ghosts suspended in isotonic NaCl/sucrose media was studied upon transient heating.

2. 2.|At 61.5°C a process of temperature accelerated disturbance of membrane permeability barrier was initiated, wich was sensed by the consequent volume changes. Concomitantly with this process the thermohaemolysis appeared as a threshold colloid-osmotic lysis.

3. 3.|The initial temperature of this successive barrier disturbance was decreased linearly by ethanol. At 18% ethanol this barrier disturbance took place at 39°C while spectrin was denaturated at about 45°C. Apparently, the spectrin denaturation was not sufficient, nor was involved in, the initiation of this membrane disturbance.

4. 4.|The membrane of cells made ion permeable in the presence of 18% ethanol by heating to 39°C contained irreversible pores with a radius of about 0.45 nm.

5. 5.|This suggests a conformational change of a protein(s) in their formation, but not spectrin nor the anion channel.

6. 6.|Using specific amino reagents it was ascertained, that a superficial NH₃⁺ group dissociable at neutral pH impeded this thermo-induced pore formation.

7. 7.|Consistent results show that this formation of membrane pores initiated at 61.5°C may be included in the still unknown mechanism of thermohaemolysis.

Some effects of thyroidectomy on growth, heat production and the thermoregulatory ability of the immature fowl (Gallus domesticus)

1. 1.|The effect of thyroidectomy at 12 days of age on weight gain, and on heat production and thermoregulatory ability of 4- to 5-week-old chickens at temperatures within and below the thermo-neutral zone was investigated.

2. 2.|Despit the absence of thyroid tissue, as demonstrated with radioiodine, a small amount of thyroxine was found in the plasma of some thyroidectomized (TX) birds.

3. 3.|Thyroidectomy depressed weight gain; pair-fed controls grew significantly faster than TX birds.

4. 4.|Resting heat production of TX birds at thermoneutrality (30°C) was depressed by 18% (P < 0.001) and body temperature by 0.4°C (P < 0.001).

5. 5.|At 12°C heat production of TX birds was similar to that of controls but the body temperature of TX birds was 0.7°C lower (P < 0.001).

6. 6.|Thyroidectomized birds were unable to regulate body temperature at 5°C even if thyroxine was provided on the day before and at the time of cold-exposure. This inability to thermoregulate was probably due to inadequate insulation and poor nutritional status.

Alteration of heat sensitivity by treatment with nonpermissive temperature or cycloheximide in temperature-sensitive CHO mutant tsH1 cell

1. 1.|The temperature-sensitive mutant CHO-tsH1 and wild type (CHO-SC) cells became thermal resistant when cells were treated for either 2 h at 39.5°C before heating at 43°C or 2 h with 10 μg/ml cycloheximide (CHM) before and during heating at 43°C.

2. 2.|There was a 2000-fold increase in survival after 2.5 h at 43°C by preincubation at 39.5°C in both cell types. There was also a 200- or 700-fold increase in survival after 2.5 h at 43°C by treatment with CHM in tsH1 or SC cell type respectively.

3. 3.|In contrast to the effects at 43°C, at 41.8°C these protective effects were not evident in tsH1 cells. In wild type, however, there was an 800- or 1800-fold increase in survival after 8 h at 41.8°C by preincubation at the temperature of 39.5°C or treatment with CHM, respectively.

4. 4.|Therefore, these results suggest that killing of tsH1 at low temperature hyperthermia (41.8°C) is probably due to denaturation of thermolabile leucyl-tRNA synthetase.

5. 5.|The denaturation of this enzyme may not be protected by inhibition of protein synthesis by preincubation at the nonpermissive temperature of 39.5°C or by CHM.

Thermosensitivity during embryonic development of Lymnaea stagnalis (Mollusca)

1. 1.|The percentage of survival after 1 hr at 40.0°C is lowest at the larval trochophore stage and at hatching of the young snail.

2. 2.|Heat resistance depends on the stage of development.

3. 3.|From the early cleavage stage onwards a higher percentage of embryos can withstand high temperature after a previous heat treatment than without it.

4. 4.|The pattern of thermosensitivity is discussed in relation to the organizational level of the stage of development.

5. 5.|It is concluded that the developing Lymnaea is a suitable system to study heat resistance and thermotolerance at the level of cells, organs and organism.

Exercise in the heat: Effects of dinitrophenol administration

1. 1.|Dinitrophenol (DNP) was administered to rats in two equal dosages (20 mg/kg, 30 min interval); the second injection was followed immediately by exercise (9.14 m/min) in the heat (30°C) or at room temperature (21°C).

2. 2.|At 21°C control (saline-treated) rats manifested a mean endurance of 94 min which was reduced to 32 min among DNP-treated animals.

3. 3.|At 30°C, control rats ran for 65 min (δT_re/min = 0.05°C) while DNP-treated animals had a mean endurance of only 12 min (δT_re/min = 0.22°C).

4. 4.|DNP-treated rats (30°C) manifested no decrements in tail-skin heat loss (δT_sk/min = 0.17°C vs 0.10°C) or saliva secretion (0.78 g/min, DNP vs. 0.19 g/min, control) for their brief treadmill duration.

5. 5.|The increased metabolic heat production of DNP severely reduced performance.

Hyperthermia-induced changes in the morphology of CHO-K1 and their refractile inclusions

1. 1.|Chinese hamster ovary cells (CHO-K1) were heated at temperatures of 42°C and above.

2. 2.|Cells were cultured in microcapillaries to eliminate handling stress, and morphological changes were observed by light microscopy.

3. 3.|Increased incidence of membrane blebbing was noted between 1 and 2 h and few cells were viable after 2 h at 43°C.

4. 4.|Morphological changes, including the appearance of potocytotic blebs, were recorded by cinemicroscopy of microcapillary cultures on a heated microscope stage.

5. 5.|Lipid-rich refractile cell inclusions changed shape before blebbing occurred.

6. 6.|Cell retraction and rearrangement of organelles seen at 1 h at 43°C are the reverse of those seen in spreading post-trypsinized cells and suggest a thermal effect on the cytoskeleton.

Temperature gradients in the nasal cavity of the rabbit

1. 1.|Temperatures at four sites along the ventral nasal concha were recorded in four unrestrained rabbits exposed to ambient temperatures from 0 to 35°C.

2. 2.|The nasal temperatures decreased and temperature gradients from proximal to distal parts of the concha increased in cold-exposed rabbits.

3. 3.|The temperature gradients increased also during panting in heat-stressed rabbits.

4. 4.|The ventral nasal concha is suggested to be an efficacious heat exchanger both in cold and hot ambient, due to its geometry and vascularization.

Polar bear thermoregulation: Effect of oil on the insulative properties of fur

1. 1.|Oil caused a substantial decrease in the insulative value of polar bear (Ursus maritimus) pelts measured in vitro.

2. 2.|Following oil contamination the calm air heat transfer coefficient increased by a factor of 2 to 5: the wind coefficient averaged 290% greater and the solar utilization increased by 55%.

3. 3.|Conductance through oil-covered furs remained high at winter temperatures (T_a = 0.6°C) but decreased with time at summer temperatures (T_a = 24.7°C).

4. 4.|The most viscous of the three oils tested had a more consistently negative effect on insulation.

Threshold temperature responses of thermosensitive neurons in guinea-pig hypothalamic slices

1. 1.|Neuronal activity in slices of the preoptic and anterior hypothalamic area of guinea-pigs during slow low-amplitude temperature changes analogous to temperature changes in the brain of endothermic animals, was extracellularly recorded.

2. 2.|42% of neurons showed threshold temperature responses. The threshold of response averaged 37.4°C for warm-sensitive neurons during warming and 37.0°C for cold-sensitive neurons during cooling.

3. 3.|The thresholds differed, on average, by 0.1°C in the same neuron at repeated temperature changes.

4. 4.|With temperatures 0.8°C above threshold on average (0.2°C in some units) neuronal activity reached a new high level that did not change either during a further exceeding of the threshold or prolonged maintenance of suprathreshold temperature.

5. 5.|The characteristics of the threshold temperature response of a hypothalamic neuron meet the criteria of thermoinduced structural rearrangements of cell membranes, caused by phase transitions of lipids, changes in protein conformation and cytoskeletal activity.

Thermohaemolysis of human erythrocytes in sucrose containing isotonic media

1. 1.|The thermohaemolysis of human erythrocytes in NaCl/sucrose isotonic media can be best accounted for in terms of the colloid-osmotic theory of haemolysis.

2. 2.|The thermohaemolysis in NaCl saline was preceded by leakage of K⁺ and cell swelling. If the inner oncotic osmoactivity was balanced with external sucrose the cells progressively shrinked losing K⁺, but the haemolysis was strongly reduced.

3. 3.|Time dependence of the shrinking of cells and one-step resealed ghosts suspended in isotonic 60 mOsm NaCl/sucrose media was studied between 50 and 58°C.

4. 4.|After a lag period for cells only, this shrinking proceeded with apparently constant rate for cells and ghosts.

5. 5.|The rate constant of shrinking for cells and ghosts obeys the Arrhenius relation, giving the value of 250 ± 15 kJ/mol for the activation energy of shrinking in both cases. This is also the case for the activation energy of the membrane ion permeability constant.

6. 6.|These results are consistent with the thermal inactivation of membrane associated protein(s) acting as a trigger for the ion permeability barrier disturbance.

7. 7.|The mid-point temperature for these membrane events was about 61°C.

Muscle temperature and muscle metabolism during short-term exercise in the goat

1. 1.|External heat exchangers acting on lower aortal blood temperature were used to dissociate hindleg muscle temperature (T_hlm) from general internal temperature (T_int) during short-term exercise of moderate intensity.

2. 2.|In series 1 39°C T_hlm was combined with 40.6°C T_int, and in series II 42°C T_hlm was combined with 39.8°C T_int.

3. 3.|At constant work rates, the 3°C difference in muscle temperature did not result in significantly different concentrations of muscle metabolites.

4. 4.|It is concluded that high local muscle temperature without general hyperthermia does not influence muscle metabolism during short-term moderate excercise.

Daphnia development and reproduction: Responses to temperature

1. 1.|The development times and reproduction were measured for Daphnia pulex and Daphnia magna from 5 to 30°C at 5°C increments.

2. 2.|The general trends for D. pulex and D. magna were for the duration of all juvenile instars to be less than that of adults and for the last juvenile (or adolescent) instar to be longer than all previous juvenile instars.

3. 3.|The number of juvenile instars both species pass through before adulthood is influenced by temperature with increasing numbers occurring at temperature extremes.

4. 4.|Duration of development time decreased over the entire range of increasing temperatures measured for D. pulex but increased for D. magna at 30°C in relation to 25°C.

5. 5.|Quadratic models were less desirable than simple linear logarithmic transformations of the form ln Y = ln a + b ln X for describing the temperature/development relationship.

6. 6.|The greatest young production occurs at 15 and 20°C with significant decreases occurring at temperatures above and below these.

7. 7.|The observed temperature-dependent phenomena an the ecological relationships for the two species are discussed.

Exercise performance of normothermic and hyperthermic rats: Effect of warm rearing

1. 1.|Hypothalamic and rectal temperatures were recorded in 8 warm-reared (wr) and 12 control rats. Rats ran to exhaustion at a constant speed of 1.5 km h⁻¹ but at a variable ambient temperature adjusted to stabilize their hypothalamic temperature at 38.0°C (normothermia) or 41.0°C (hyperthermia). Blood lactate concentrations were determined before and after exercise.

2. 2.|Exercise caused exhaustion in normothermic control rats after 62.08 ± 5.43 min and in wr rats after 29.64 ± 2.09 min.

3. 3.|Hyperthermia shortened to one half (to 12.24 ± 1.36 min) and to one fourth (to 16.15 ± 1.20 min) the endurance time in wr and control rats, respectively.

4. 4.|There were no correlations between lactate concentraion and hyperthermia or endurance time.

5. 5.|In conclusion, in rats and other animals which have safe refuges, hyperthermia interferes with the ability to continue exercising.

Cardiovascular and thermoregulatory responses to repeated anticholinesterase administration

1. 1.|Pyridostigmine administration decreased resting heart rate by 11 ± 7 beats/min and resting oesophageal temperature by 0.23 ± 12°C after 50 h (P < 0.05). In addition, red blood cell cholinesterase activity was decreased an average of 43 ± 7% after 50 h of pyridostigmine treatment.

2. 2.|The lower heart rates and core temperatures at rest were continued during high intensity exercise in a 35°C environment. Whole body sweating was 12 ± 18% higher (P = 0.20) during exercise in the heat after 50 h of pyridostigmine treatment.

3. 3.|Repeated anticholinesterase administration had little effect on cardiovascular and thermoregulatory responses during high intensity exercise.

Effect of temperature on growth and bioenergetics of a tropical moth

1. 1.|Larval development and metamorphosis of Achaea junta were prolonged at 22°C, compared to 27, 32 and 35°C.

2. 2.|Overall rates of consumption, assimilation, production and metabolism of the larvae increased with temperature.

3. 3.|Efficiencies of assimilation and conversion of the digested food were significantly altered by life stage and temperature.

4. 4.|About 60% of the pupal energy was transferred to the imago at the tested temperatures.

The combined effects of ambient temperature and enforced sustained swimming activity on body temperatures of arctic charr (Salvelinus alpinus L.)

1. 1.|The difference between tissue temperatures and ambient water temperatures (ΔT) of the ectothermic Arctic charr (Salvelinus alpinus L.) ranged between 0.2 and 0.6°C.

2. 2.|For fish held at 5.7°C there were no significant differences in ΔT of exercising fish and those of controls.

3. 3.|By contrast, for fish held at 1.7°C sustained exercise led to a significant increase in ΔT of all body compartments compared with fish held in standing water (controls).

4. 4.|It is suggested that Arctic charr are capable of a limited control of metabolic heat exchange between body compartments and surrounding water when subjected to sustained exercise and ambient temperatures <2°C.

Thermal resistance of the ciliary activity in the gills of the fresh water mussel Anodonta anatina

1. 1.|The thermal resistance of the activity of frontal cilia in the median gills of the fresh water mussel Anodonta anatina was studied.

2. 2.|The resistance acclimation appeared in 2 days in the gills of intact animals, but not in the isolated gills kept at 4, 14 and 24°C, for between 1 to 3 days.

3. 3.|Warm-acclimation increased the ACh sensitivity of the gills of intact mussels.

4. 4.|Isolation of the gills enhanced the thermal resistance.

5. 5.|ACh, choline and tetramethylammonium enhanced the thermal resistance in the isolated gills. whereas atropine and physostigmine diminished it.

6. 6.|It is concluded that in A. anatina the control if the thermal resistance is probably neural.

A central excitatory serotonergic or serotonergic-like synapse on the pathway to heat production in the sheep

1. 1.|Intraventricular injections of serotonergic agonists and receptor blockers were given to sheep to determine whether the central nervous pathway mediating the drive to heat production involves serotonergic synapses.

2. 2.|At 15°C ambient temperature (T_a), 5-hydroxytryptamine (5-HT) at all doses tested, and norfenfluramine (NF) in low doses increased heat loss and decreased rectal temperature (T_re); lysergic acid diethylamide (LSD-25) and methysergide prevented these effects.

3. 3.|AT 0°C T_a, 5-HT, even in high doses failed to increase heat production but NF increased heat production and T_re.

4. 4.|The results suggest the effects of NF and LSD-25 on heat production may be related to synapses activated by an indoleamine other than 5-HT.

Biochemical changes in tissue composition of Periplaneta americana (Linn.) acclimated to high and low temperatures

1. 1.|Cold acclimation apparently favours an increase of water content in fat body, but not in coxal muscle, of cockroaches.

2. 2.|A remarkable enhancement in the accumulation of total protein in fat body characterizes the cold acclimation of cockroaches, particularly adult males (175% increase in protein/DNA ratio). The increase in protein content of coxal muscle during acclimination to 15°C, observed in nymphs (16%) and males (16%) but not in females, is less pronounced than that of fat body.

3. 3.|A diminution (28–32%) in the free amino acid/DNA ratio due to cold acclimation has been recorded in both coxal muscle and fat body of nymphs and females, but not in males.

4. 4.|No qualitative change occurs in the free amino acid spectrum of haemolymph and tissues of this insect during acclimation to 15 and 35°C.

5. 5.|An augmentation (15–30%) of the RNA/DNA ratio occurs in fat body and coxal muscle of nymphs and males but in fat body alone of females following cold acclimation.

6. 6.|The glycogen reserve has been shown to increase by up to 30% in fat body and coxal muscle of cold acclimated cockroaches compared to warm acclimated ones.