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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Black-box models of thermoregulatory control have gained increasing importance in describing the properties of the biological thermostat and in devising working hypotheses for further experimental analysis. Incorporation of knowledge acquired independently from the systems analysis approach into black-box models of thermoregulation has proven useful in improving their predictive ability. The pieces of "borrowed knowledge" from independent analysis which are currently utilized in devising models of homeothermic thermoregulation comprise: the proportional control property of the biological thermostat, the Sherringtonian principles of synaptic interaction, the multiple input control of thermoregulatory effectors with differential input-effector coupling, the lack of significant thermosensory contribution from the hypothalamus in birds, the existence of warm and cold receptors and the thermal characteristics of their responses, and the Q10-type temperature dependence of temperature signal transmission within the central nervous system. Consideration of these pieces of borrowed knowledge has resulted in black-box models of temperature regulation in which explicit set-point terms are avoided.
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PMID:Are black-box models of thermoregulatory control obsolete? The importance of borrowed knowledge. 375 Nov 39

Rates of force development, contraction and relaxation of vertebrate skeletal muscle are temperature dependent with Q10 values of approximately 2. Maximal forces developed have a low or negative thermal dependence. The functional basis of these patterns is poorly understood. Muscle performance generally does not acclimate. There appears to have been some evolutionary adaptation among species and classes to different thermal regimes, such that muscles from cold-adapted species maintain better mechanical performance at low temperatures than do those from warm-adapted animals. However, rate processes remain strongly thermally dependent even in animals with low or variable body temperatures. This thermal dependence of muscle in vitro is reflected in behavioural performance: maximal force generation in vivo is temperature independent and time-dependent activities are more rapid at higher muscle temperatures.
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PMID:Temperature and muscle. 387 78

Conductive properties of muscle fibres from green sunfish (Lepomis cyanellus) acclimated to different temperatures were examined. The relative membrane permeability to chloride and potassium ions, PCl/PK, measured at acclimation temperature, was approximately 7.0 after acclimation at 25 degrees C and 1.3 after acclimation at 7 degrees C. This difference was due to a six-fold reduction in the membrane chloride conductance upon acclimation to 7 degrees C as compared to 25 degrees C-acclimated fibres. Mean (+/- S.E.M.) values of the chloride conductance were 554 +/- 68 microseconds cm-2 in warm-acclimated sunfish, and 75 +/- 9 microseconds cm-2 in cold-acclimated sunfish. Membrane capacitance also differed significantly between the two acclimation groups. When the temperature was varied acutely, the magnitude of the chloride conductance exhibited a maximum Q10 of only 1.9, compared with a Q10 of 3.0 associated with acclimation. Upon transferring 25 degrees C-acclimated sunfish to holding tanks at 7 degrees C, the total membrane resistance exhibited a sigmoidal increase over about 14 days, and a steady membrane capacitance was achieved in about 10 days. For 7 degrees C-acclimated sunfish, transferred to 25 degrees C, resistance showed a sigmoidal decrease over 10 days and capacitance was steady after 8 days. The results indicate that thermal acclimation of the muscle membrane involves cellular regulatory processes which underlie significant changes in the electrical properties of the fibre.
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PMID:The effects of temperature acclimation on the resting membrane of skeletal muscle fibres from green sunfish. 400 10

1. Differential thermal acclimatory responses of maximal catalytic rates (Vmax) of digestive enzymes have been measured in both sexes of Periplaneta americana adapted to 16 and 32 degrees C. 2. Salivary amylase of females and gastric protease of males exhibit "translational" acclimation, the former showing a "complete" but the latter only a "partial" compensation. The value of Q10 is not altered in the adaptive response. 3. An alteration of the thermal coefficient is evidenced by the "translational-cum-rotational" compensation of gastric amylolytic activity, with significant warm acclimation but no cold acclimation in both sexes. 4. Gastric protease of female cockroaches and gastric lipase of both sexes are characterized by the lack of an adaptive compensation to temperature, while salivary amylase of male appears to manifest an "inverse" acclimation. 5. Sexual dimorphism in the levels of the activities and in the patterns of thermal acclimation of the digestive enzymes is indicated.
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PMID:Compensations for temperature in the activities of digestive enzymes of Periplaneta americana (L.). 617 77

1. Ninety-six neurones in forty-six explant tissue cultures of rat medial basal hypothalamus (m.b.h.) and preoptic area (p.o.a.h.) were subjected to thermal stimulation. 2. Neuronal response to temperature was determined on the basis of an extrapolated Q10 calculated from the regression line relating mean spontaneous activity to bath temperature. 3. Thermal stimulation (28-41 degrees C) of p.o.a.h. cultures resulted in the identification of three distinct groups of neurones: (1) temperature-insensitive (0.5 less than or equal to Q10 less than or equal to 2), (2) warm-sensitive (Q10 greater than 2), and (3) cold-sensitive (Q10 less than 0.5). 4. No temperature-sensitive neurones were identified in m.b.h. cultures. 5. In the presence of a medium which effectively blocks synaptic transmission (12 mM-Mg2+ and 0.25 mM-Ca+) the sensitivity of both warm- and cold-sensitive neurones was preserved. 6. These data indicate that thermosensitivity is a characteristic not only of the preoptic neuronal network in vitro but also is an intrinsic characteristic of individual neurones.
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PMID:Electrophysiological analysis of neuronal thermosensitivity in rat preoptic and hypothalamic tissue cultures. 628 24

Potassium currents were measured using the three-microelectrode voltage-clamp technique in rat omohyoid muscle at temperatures from 1 to 37 degrees C. The currents were fitted according to the Hodgkin-Huxley equations as modified for K currents in frog skeletal muscle (Adrian et al., 1970a). The equations provided an approximate description of the time course of activation, the voltage dependence of the time constant of activation (tau n), and the voltage dependence of gK infinity. At higher temperatures the relationship between gK infinity and voltage was shifted in the hyperpolarizing direction. The effect of temperature on tau n was much greater in the cold than in the warm: tau n had a Q10 of nearly 6 at temperatures below 10 degrees C, but a Q10 of only approximately 2 over the range of 30-38 degrees C. The decreasing dependence of tau n on temperature was gradual and the Arrhenius plot of tau n revealed no obvious break-points. In addition to its quantitative effect on activation kinetics, temperature also had a qualitative effect. Near physiological temperatures (above approximately 25 degrees C), the current was well described by n4 kinetics. At intermediate temperatures (approximately 15-25 degrees C), the current was well described by n4 kinetics, but only if the n4 curve was translated rightward along the time axis (i.e., the current had a greater delay than could be accounted for by simple n4 kinetics). At low temperatures (below approximately 15 degrees C), n4 kinetics provided only an approximate fit whether or not the theoretical curve was translated along the time axis. In particular, currents in the cold displayed an initial rapid phase of activation followed by a much slower one. Thus, low temperatures appear to reveal steps in the gating process which are kinetically "hidden" at higher temperatures. Taken together, the effects of temperature on potassium currents in rat skeletal muscle demonstrate that the behavior of potassium channels at physiological temperatures cannot be extrapolated, either quantitatively or qualitatively, from experiments carried out in the cold.
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PMID:A quantitative study of potassium channel kinetics in rat skeletal muscle from 1 to 37 degrees C. 630 31

Single fibres or small fibre bundles were dissected from twitch muscles of frogs and washed in low Cl-solutions. Contractures were provoked by 122.5 mM K+. At room temperature (17-20 degrees C) the contracture duration was about 1.5 s in the absence of divalent cations and about 3 s in the presence of 2 mM Ca2+. Contractures were prolonged when Ca2+ was replaced by Ni2+ showing that inward Ca current was not the factor responsible for the contracture prolongation. K contracture duration was prolonged in the cold (3 degrees C) by a factor of about 4 in the presence of non-permeating divalent cations (Ni, Co), when 0.1 mM La3+ was applied together with 2 mM Ca2+, and in the virtual absence of divalent cations. The contractures were prolonged in the cold by a factor of 6 or more in the presence of permeant divalent cations (Ca, Sr, Ba, Mg, and Mn at 8 mM). Diffusion of divalent cations in the transverse tubules of the muscle fibres was shown to have a Q10 similar to that in free solution. It was concluded that inward current of divalent cations may shorten contracture duration by causing ionic depletion of the transverse tubules.
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PMID:Influence of divalent cations on potassium contracture duration in frog muscle fibres. 631 3

Two patients were rewarmed from hypothermia (esophageal temperature 27.2 degrees C, 27.5 degrees C respectively). The first case suffered from head-injury after alcohol ingestion and was deeply comatose. A metabolic or cardiovascular regulatory response to cold was not observed in this patient. The relationship between esophageal temperature and whole-body-oxygen consumption was quantified with a Q10 of 2.75 during rewarming (27.2-37.2 degrees C). His epinephrine levels were greatly elevated to 1,000 pg/ml whereas norepinephrine levels were only moderately increased to 250 pg/ml. Premature ventricular contractions (PVCs) during intubation or from the pulmonary artery catheter were not observed. The second patient was a 87 year old man with accidental hypothermia. He exhibited shivering at an esophageal temperature of 27.5 degrees C which indicated persistent thermoregulation. In contrast to the first case his norepinephrine levels were elevated to 1,500 pg/ml and his epinephrine levels only to 450 pg/ml. After onset of surface rewarming an additional increase in norepinephrine levels was observed and an increasing rate of PVC's (15/min) recorded, which ceased when temperature returned to normal. Our observations indicate that part of the cardiac complications during rewarming from deep hypothermia may result from thermoregulation and additional catecholamine liberation.
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PMID:[Rewarming from moderate to deep hypothermia: plasma catecholamine content, metabolism and circulatory function. 2 case reports]. 648 85

In conscious rabbits with chronically implanted hypothalamic thermodes sustained panting was induced by exposure to 39 degrees C ambient temperature. Core temperature (Tc) measured in the esophagus was maintained at hyperthermic levels of about 41.1, 40.2 and 39.2 degrees C by controlled heat extraction with a cooling thermode inserted into the colon. Hypothalamic temperature (Thy) was varied from its control value of 39.1 degrees C for periods of 2-3 min by altering the temperature of the water perfusing the thermode in a stepwise fashion from 39 degrees C to mostly lower and sometimes higher values. In several experiments a period of moderate hypothalamic cooling was immediately followed by a period of strong cooling. Breathing frequency (BF) was continuously recorded as an index for thermal panting. Panting rate was positively correlated with Tc, maximum panting being attained at 41.1 degrees C Tc and normal Thy. Lowering Thy reduced and elevating Thy stimulated panting at constant Tc. At each level of Tc the inhibitory effect of lowering Thy on BF was found to be diminished at strong degrees of hypothalamic cooling resulting in non-rectilinear relationships between BF and Thy. In the experiments with two-step hypothalamic cooling BF tended to rise in some trials rather than to decrease further with the transition from moderate to strong hypothalamic cooling. The relationships between Tc, Thy and BF could be satisfactorily described by each of two mathematical models, the one presuming a Q10 of 1.5 for cold and a Q10 of 8.3 for warm signal transmission in the hypothalamus, the other presuming a Q10 of 3.5 for cold and a Q10 of 2.5 for warm signal transmission and, additionally, the existence of hypothalamic thermosensors.
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PMID:Interaction between hypothalamic and extrahypothalamic body temperatures in the control of panting in rabbits. 662 21

Incorporation of 14C-leucine and 3H-alanine into TCA-precipitable protein. TCA-soluble protein, and antifreeze glycoproteins (AFGP) was measured in isolated hepatocytes from Pagothenia borchgrevinki Boulenger following acclimation to -1.5 degrees C and +4 degrees C. the rate of 3H-alanine incorporation into AFGP followed Michaelis-Menten kinetics with a Vmax of 4.8 nM X mg protein-1 X h-1 at -1.5 degrees C and 7.5 nM X mg protein-1 X h-1 at +4 degrees C. Km values were 27.9 microM and 41.7 microM at -1.5 degrees C and +4 degrees C, respectively. Incorporation of 14C-leucine into TCA-precipitable protein also showed Michaelis-Menten kinetics with a Vmax of 20 nM X mg protein-1 X hr-1 at 1.5 degrees C and 32.3 nM X mg protein-1 X hr-1 at +4 degrees C. Km values were 83.3 microM at -1.5 degrees C and 125 microM at +4 degrees C. AFGP synthesis was monitored over a 120-h period by radioimmunoassay in cultures of hepatocytes from cold acclimated fish (-1.5 degrees C) incubated at both -1.5 degrees C and +4 degrees C. The estimated Q10 for AFGP from these data is 3.23. Polyacrylamide gel electrophoresis of antifreeze glycoproteins produced by isolated hepatocytes showed that all four antifreeze fractions normally present in the serum of P. borchgrevinki are also synthesized by isolated hepatocytes. The two major conclusions from these experiments were that 1) P. brochgrevinki, unlike many northern fishes, does not show thermal acclimation, and 2) environmental factors responsible for modification of peptide antifreeze synthesis in northern fishes do not elicit changes in AFGP synthesis in P. borchgrevinki.
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PMID:Characterization of glycoprotein antifreeze biosynthesis in isolated hepatocytes from Pagothenia borchgrevinki. 707 67


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