Activity of warm receptors inBoa constrictor raised at various temperatures

Nine young specimens ofBoa constrictor were raised for 4 years in a climatic chamber at an ambient temperature of 30°C under artificial illumination. Seven boas were raised at 23°C under the same conditions. At the end of the adaptation period, mean body weight of the warm adapted boas was 9.6±0.8 kg and that of the cold adapted ones 5.9±0.3 kg.Static and dynamic activities of single specific trigeminal warm fibers were recorded when applying static temperatures of 20, 23, 26, 29, 32, 35 and 38°C and dynamic warming steps of 3°C, the initial temperatures being 20, 23, 26, 29, 32 and 35°C. Eighty-nine warm fibers were examined in the warm adapted and 62 fibers in the cold adapted group.The average static frequencies between 29 and 35°C were higher in the warm adapted animals, the respective values for both groups at 32°C being 16.5 and 12s^–1. The average peak frequencies for dynamic warming were 80s^–1 for both groups, but the temperature of the dynamic maximum was shifted from 32°C in the warm adapted to 26°C in the cold adapted boas. At 32 and 35°C the average peak frequencies were higher in the warm adapted animals.The whole fiber population contained various groups with static maxima between 23 and 35°C. Long-term adaptation modified mainly the static and dynamic discharge of the low-temperature fibers. The fiber group with a static maximum at 29°C showed a crossing of the static and dynamic frequency-temperature curves. In the higher temperature range the warm adapted animals had a higher and in the lower temperature range a lower static and dynamic frequency.     

Static and dynamic activity of cold receptors in cats after long-term exposure to various temperatures

Ten cats were adapted for 4.7 years in a climatic chamber to an ambient temperature of 5°C and 8 cats to 30°C under artificial illumination and food ad libitum. Cats living at 5°C had 15.2±0.5 mean nasal and 38.0±0.3°C mean rectal temperature; the corresponding values for cats living at 30°C were 31.0±0.4°C and 38.3±0.1°C.Static and dynamic activities of single specific cold fibers from the nose were recorded when applying static temperatures of 40, 35, 30, 25, 20, 15 and 10°C and dynamic cooling steps of 5°C starting from static temperatures between 40 and 15°C. In each group, a population of 100 cold fibers was examined.The average static frequencies between 35 and 20°C were slightly but not significantly lower in the cold adapted group, the respective values for both groups at 30°C being 5.6 and 6.5s^–1. The average dynamic maxima were considerably lower in the cold adapted group throughout the whole temperature range, the values at 30°C being 44 and 61s^–1, respectively. The difference between the dynamic frequency-temperature curves of both fiber populations was highly significant (P<0.001).The distribution of static maxima of individual cold fibers as well as the distribution of fibers with static bursts was nearly identical for both groups, whereas the distribution of dynamic maxima and dynamic bursts was significantly shifted to lower temperatures in the cold adapted group.Seven sub-groups of cold fibers were formed according to their static maximum at temperatures between 40 and 10°C. The most pronounced adaptive modification was a significantly lower dynamic peak frequency of the sub-groups with static maxima at 15, 20, 25, 35 and 40°C in the cold adapted animals.     

Functional differences in type-I fibres from two slow skeletal muscles of rabbit

The present study addressed the question of whether the slow fibres of mammalian skeletal muscle, containing the myosin heavy chain MHCI (type-I fibres), are a functionally homogeneous population. We compared various properties of Ca²⁺-activated, skinned, type-I fibres from the soleus and semitendinosus muscles of a rabbit. Soleus type-I fibres showed significantly faster kinetics of stretch activation, measured as the time-to-peak of the stretch-induced, delayed force increase, t₃, than semitendinosus fibres (1239±438 ms, n=136, vs. 1600±409 ms, n=208 respectively) (means±SD, 22 °C). Similarly, the speed of unloaded shortening at 15 °C was faster in soleus than in semitendinosus fibres [0.79±0.16 fibre lengths (FL) s^–1, n=44, vs. 0.65±0.15 FL s^–1, n=35 respectively]. The kinetics of stretch activation were more temperature sensitive in semitendinosus than in soleus fibres. Finally, the generation of steady-state isometric force was more sensitive to Ca²⁺ in semitendinosus than in soleus fibres: [pCa₅₀ (–log [Ca²⁺] for half-maximal activation) at 22 °C: 6.29±0.15, n=28, vs. 6.19±0.10, n=18 respectively]. These results suggest strongly that there is no functional homogeneity within type-I fibres of different muscles. The observed differences might reflect the existence of more than one functionally different slow myosin heavy chain isoforms or other modifications of contractile proteins.     

Diffusivity and Solubility of Nitric Oxide in Water and Saline

Aqueous diffusivities and solubilities of NO were determined by using a chemiluminescence detector to measure time-dependent fluxes across stagnant liquid films confined between polydimethylsiloxane membranes. The NO diffusivities in pure water and PBS at 25C were found to be (2.21 ± 0.02) × 10^–5 cm² s^–1 and (2.21 ± 0.04) × 10^–5 cm² s^–1, respectively. Although lower than most previous values for NO at room temperature, these diffusivities are very similar to those for O₂, as one would expect. Extrapolation to 37°C yielded a value of 3.0 × 10^–5 cm² s^–1. The solubility of NO in water at 25°C was (1.94 ± 0.03) × 10^–6 mol cm^–3 atm^–1, in agreement with the literature. This agreement, along with the excellent fits obtained to the transient flux data (<4% rms error in each experiment), supports the validity of the simultaneously measured diffusivity. The solubility of NO in PBS at 25°C was (1.75 ± 0.02) × 10^–6 mol cm^–3 atm^–1. The modest (10%) reduction in solubility relative to that in pure water is consistent with the usual effects of salts on gas solubilities.     

The effect of temperature on contractile activation of intact and chemically skinned ‘catch’ muscle fibre bundles of Mytilus edulis

Summary The effect of temperature (5–35° C) on maximum force production was examined in intact and chemically skinned muscle fibre bundles (10–25 fibres) from the anterior byssus retractor muscle of Mytilus edulis. In intact fibre bundles, 10 m acetylcholine induced a tonic contraction which had a magnitude of 65.4±4.0 N cm^-2 (n=30) at 23° C. Activation by caffeine (20 mm) produced a force response which was 157.1±7.9% (n=16) of the acetylcholine response at 23° C and acetylcholine and caffeine together produced force which was not significantly different from the response to caffeine alone. At 5° C the acetylcholine and caffeine responses were decreased by 9.6±3.4% (n=6) and 14.6±2.8% (n=8) compared with the respective responses at 23° C. However, there was no significant reduction of the response induced by the combined action of acetylcholine and caffeine when the temperature was decreased from 23° C to 5° C. The 20–80% of peak force activation time increased by about one order of magnitude for all acetylcholine, caffeine and combined acetylcholine-caffeine-induced responses when the temperature was decreased from 23–5° C. Repeated exposure of the intact preparation to caffeine caused a marked decrease in the caffeine-induced response (complete abolition of force after the third exposure to caffeine), but the response to caffeine could be fully restored following one acetylcholine-induced activation. The maximum Ca²⁺-activated force after skinning the preparation with saponin was not significantly different from the caffeine or combined acetylcholine-caffeine-induced responses before skinning. In the saponin skinned fibre preparation a drop in temperature from 23° C to 15° C or 5° C decreased the maximum Ca²⁺-activated force by 13.2±1.4% (n=8) and 41.4±3.1% (n=5) respectively. The activation time between 20–80% of the peak Ca²⁺-activated force increased at 15° C and 5° C by a factor of 1.5±0.1 (n=5) and 6.8±1.1 (n=5) respectively when compared to corresponding values at 23° C. The relaxation half-time decreased by a factor of 1.7±0.2 (n=5) and 3.0±0.2 (n=5) at 15° C and 5° C respectively compared with that at 23° C. It was possible to distinguish between the temperature effects on the contractile apparatus per se and the Ca²⁺ regulatory system with the results indicating that the contractile apparatus was more sensitive to a change in temperature than the Ca²⁺-regulatory system. Increasing the temperature to 35° C irreversibly affected the ability to develop and maintain force in both intact and skinned muscle preparations. These results indicate that: (1) acetylcholine does not fully activate the intact catch muscle at 23° C; (2) acetylcholine is able to replenish the internal stores after depletion by caffeine; (3) compensatory mechanisms which oppose the inhibitory effect of lower temperatures on the contractile apparatus and the Ca²⁺-regulatory system must be operating in the intact fibre preparations.     

Characterization of the sodium currents in isolated human cardiocytes

The whole-cell recording technique was used to register Na⁺ currents from 403 atrial cardiocytes isolated from 80 human biopsies. With intracellular [Na⁺] ([Na⁺]_i) raised to 70 mM, and at physiological extracellular [Na⁺] ([Na⁺]_e, 145 mM) and room temperature, the Na⁺ currents were small enough for the error of the voltage clamp not to exceed 2 mV (series resistances 0.4–2 M). The threshold potential of the Na⁺ current was –64.0±7.7 mV. The peak amplitude was at –30.0 ±6.2 mV. The time course of fast inactivation was satisfactorily described with a single exponential. The time constant of inactivation was 2.0 ms at –55 mV and asymptotically approached 0.2 ms at positive membrane potentials. The steady-state inactivation curve was well fitted by a single Boltzmann distribution. Increasing the prepulse duration from 32 to 512 ms shifted the inflexion point of the curve from –61.7 ±6.4 to –72.2±2.6 mV. The time course of slow inactivation was also well described by a single exponential, the time constant ranging from 76.1±29.3 ms at –115 mV to 18.6 ±7.8 ms at –55 mV. Fitting the time course of recovery from inactivation required two time constants. At a recovery potential of –135 mV these were 1.6±0.2 and 8.6±2.9ms and 15.9±9.4 and 53.2±33.3 ms at –95 mV. A 50% block of the Na⁺ currents was achieved by tetrodotoxin at 10 M. It is concluded that the properties of human cardiac Na⁺ channels are similar to those of the juvenile Na⁺ channels of human skeletal muscle.     

Eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man

Summary The primary purpose of this investigation was to study the eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man using a recently developed combined isometric, concentric and eccentric controlled velocity dynamometer (the SPARK System). A secondary purpose was to compare the method error associated with maximal voluntary concentric and eccentric torque output over a range of testing velocities. 21 males (21–32 years) performed on two separate days maximal voluntary isometric, concentric and eccentric contractions of the quadriceps femoris at 4 isokinetic lever arm velocities of 0° · s^–1 (isometric), 30° · s^–1 120° · s^–1 and 270° · s^–1. Eccentric peak torque and angle-specific torques (measured every 10° from 30° to 70°) did not significantly change from 0° · s^–1 to 270° · s^–1 (p>0.05) (with the exception of angle-specific 40° torque, which significantly increased;p<0.05). The mean method error was significantly higher for the eccentric tests (10.6%±1.6%) than for the concentric tests (8.1%±1.7%) (p<0.05). The mean method error decreased slightly with increasing concentric velocity (p>0.05), and increased slightly with increasing eccentric velocity (p>0.05). A tension restricting neural mechanism, if active during maximal eccentric contractions, could possibly account for the large difference seen between the present eccentric torque-velocity results and the classic results obtained from isolated animal muscle.     

Factors affecting the development ofDipylidium caninum inCtenocephalides felis felis (Bouché, 1835)

Ctenocephalides felis felis larvae were infected withDipylidium caninum at a range of temperatures from 20°–35°C at 3 mm Hg saturation deficit (SD) and 30°C at 8 mm Hg SD. Hosts were subsequently dissected at 6, 9 and 12 days after infection. Four replicate, experiments were performed and results of development, and host reactions analysed by the Genstat computer programme. These were found to depend on the temperature and saturation deficit of the environment. Unlike previous findings, parasite development and host reaction were found to be independent of host development. Host reaction was more marked and prolonged at 20°–25°C than at higher temperatures.No perceptible growth of the parasite occurred at 20°C. The development patterns of growth at the higher temperatures were similar but shifted in time so that faster growth occurred at higher temperatures. Rate of growth was fastest at 35°C, despite the fact that this temperature was unfavourable to the hosts, all of which died at the time of pupation.     

Influence of the thyroid state on the calcium transient in ventricular muscle

The purpose of this study was to determine the influence of thyroid hormone on tension development and the intracellular calcium transient in mammalian ventricular muscle. A hyperthyroid (H) state was induced in ferrets by subcutaneous injection ofl-thyroxine, 0.3 mg/kg daily, for 2–3 weeks. One-half of the age matched control group (C) were injected with vehicle. Aequorin was loaded into the cells of ferret papillary muscles by a chemical procedure. The muscles were stimulated at 0.33 Hz and isometric tension and the calcium transient were simultaneously recorded at 30°C. Peak isometric tension in mN/mm² (±SD) was 15.4±7.2 and 16.2±7.9 for C (n=8) and H (n=9) respectively. The time to peak tension and time to 80% relaxation from peak of tension were reduced by 22% and 28% respectively in H compared to C. After stimulation, the calcium transient reached a maximum in 56±6 ms in C and in 47±5 ms in H. The time to 80% decay of the peak calcium transient was 95±8 ms and 68±5 ms for C and H respectively. The ratio of the aequorin luminescence at the peak of the calcium transient over the calculated maximum luminescence,L _max, were compared and they were not different. At 22°C Log (L/L _max) was –3.3±0.1 in C (n=4) and –3.4±0.3 in H (n=3). These results indicate that the thyroid state influences the time course of the calcium transient and are consistent with the abbreviation in the duration of contraction that is observed in the hyperthyroid state.     

Afferent activity recorded during rotation from single fibres of the posterior nerve in the isolated frog labyrinth

Summary EPSPs and spikes were recorded at rest and during rotation from single fibres of the posterior nerve in the isolated frog labyrinth. The spike discharge properties of 57 units were examined at rest and during repetitive acceleratory-velocity steps. Forty of these units were subjected to excitatory steps of 5–12 s duration and 45% displayed an evident discharge adaptation. In the non-adapting units, the excitatory response also deviated from that expected on the basis of the torsion-pendulum model and exhibited an exponential time-course in only 36% of the fibres examined. The time constant T₂ of the response rising phase was significantly longer than that of the decay (2.5 s versus 1.7 s). When all the 57 units were considered, a linear behaviour was found in 67%. The average gain in these linear units was 1.9 ± 1.4 spikes · s^–1/deg · s^–2. Adaptive fibres exhibited a lower resting firing rate and a higher gain (3.8 spikes/s and 2.3 spikes · s^–1/deg · s^–2, respectively) when compared with the non-adapting ones (7.1 spikes/s and 1.5 spikes · s^–1/deg · s^–2). An undershoot was present in 57% of the units; it increased with acceleration and was not strictly related to adaptation. Fifteen of the 40 units tested with the 5–12 s duration excitatory steps survived repeated inhibitory accelerations of the same duration. In these units a marked response asymmetry was evident since their resting activity could be abolished by accelerations not larger than 10 deg/s². In 40% of the units inhibited by acceleration the mean response was proportional to the stimulus logarithm, while the others saturated for weak stimulations. A consistent overshoot of the discharge was evident in most of the units (60%). Analysis of the EPSP emission rates demonstrates that even a 10–20% increase in their frequency during excitation results in a two-three fold increase in the corresponding spike frequency. Similarly, a decrease of 15–35% in their numbers during inhibition is sufficient to completely block the spike firing. These findings reveal the high sensitivity of the afferent synapse, spike discharge being modulated by slight modifications in the release of the excitatory transmitter.     

Static and dynamic activity of warm receptors in Boa constrictor

Summary Afferent impulses from multi- and single-fiber preparations of the trigeminal nerve inBoa constrictor were recorded during exactly controlled thermal stimulation of the receptive field in the labial region. At constant temperatures in the range between 18 and 37°C, multi-fiber preparations showed a continuous discharge with a maximum around 30°C. Dynamic warming caused a high increase of the discharge, whereas dynamic cooling led to a complete inhibition. No cold-sensitive fibers have been found. Mechanical stimulation elicited large spikes from specific mechanoreceptors.Single-fiber preparations from labial warm receptors did not respond to mechanical stimulation. Their discharge was always regular at constant temperatures. The average frequency of a warm receptor population was zero at about 18°C, reached a maximum of 13 sec^–1 at 30°C and fell again to zero at 37°C. In addition, a few warm receptors increased their static discharge with temperature up to 36°C, the highest frequency being 38 sec^–1. Stepwise warming by T=+5°C caused a marked overshoot in frequency, after which the discharge usually fell to a minimum and then rose again to a new static level. Stepwise cooling by T=–5°C led to a transient inhibition of activity followed by an increase until the new static level was reached. In the first group of warm receptors the height of the dynamic overshoot varied with the adapting temperature, the largest average overshoot of 160 sec^–1 occurring at an adapting temperature of 30°C. These receptors have their static maximum as well as their highest dynamic sensitivity in the temperature range of the natural tropical habitat of Boidae.Supported by a grant from the Deutsche Forschungsgemeinschaft     

A Heat Transfer Model of Thermal Balloon Endometrial Ablation

A heat transfer model was developed for thermal balloon endometrial ablation treatment for menorrhagia. The model includes heat conduction through the uterus wall, cooling due to blood perfusion through the uterine tissue and the contribution of metabolic heat generation. A parameter sensitivity study indicated that metabolic heat generation had a minimal effect, but model predictions were sensitive to blood perfusion rate. However, within the range of expected perfusion rates, the model calculates damage depths (3–6 mm) close to the range for effective treatment. Using a blood perfusion rate of 0.0028 m _t ³ m _b ^-3 s _s ^-1 the predicted burn depth (4 mm) correlated well with experimental measurements (4.2 ± 0.6 mm) reported elsewhere for a treatment temperature of 92°C and time of 6 mins (Neuwirth, R. S. et al. The endometrial ablator: A new instrument. Obstet. Gynecol. 83:792–796, 1994). If no vaporization of water in the tissue occurs, the model predicts that the same burn depth of 4 mm can be obtained with increased treatment temperature (130°C) and shorter treatment time (1.4 min). Steeper temperature profiles through the uterine wall suggest that, in the absence of other changes due to higher temperatures, the deeper layers of the myometrium and the serosa would be protected from thermal damage when using higher treatment temperatures for a shorter duration. However, if vaporization occurs at 105°C, the model predicts little benefit in using treatment temperatures above 120°C up to 160°C. For further validation of the model, in vivo studies using the high temperature treatments are needed to measure temperature profiles through the uterine wall, blood perfusion rates, and the other effects of temperature on uterine tissue. © 2001 Biomedical Engineering Society. PAC01: 8719Pp, 8710+e, 8780-y, 8719Tt     

Propagation of Telotylenchus loofi on plant callus tissues

Summary Attempts have been made to cultivate Telotylenchus loofi on plant callus tissues at different temperature ranges. Although the subjection of cultures to 17–20, 30–35 and 35–40° C temperatures did not prove a handicap in nematode propagation, huge populations could only be obtained at 25–27° C. The temperatures below 17° C and beyond 40° C were found unsuitable for cultivation of T. loofi.

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Zusammenfassung Es wurden Versuche durchgeführt, Telotylenchus loofi an Pflanzen Callusgewebe bei verschiedenen Temperaturbereichen zu vermehren. Zuchttemperaturen zwischen 17 und 20°, 30 und 35° und 35–40° ließen zwar keine wesentliche Beeinträchtigung der Vermehrung erkennen, aber die besten Zuchtbedingungen lagen bei 25–27° C. Temperaturen unter 17° C und über 40° C waren für die Kultur von T. loofi ungeeignet.

     

Lowering of skin temperature decreases isokinetic maximal force production independent of core temperature

Based on studies using maximal isometric contractions, it is suggested that fatigue may be elicited due to hyperthermia-induced impairments in central neuromuscular activation. We investigated the effects of passive hyperthermia on isokinetic maximal force production. Twenty young healthy males [peak oxygen uptake 52.9 (6.8) ml kg^–1 min^–1, body fat 11 (5)%] were passively warmed in a hot (42°C) water bath to rectal temperature (T_re) of 39.5°C and then cooled back to 38.0°C. At 0.5°C intervals, they performed two maximal voluntary knee extensions each at 60, 120, and 240 s^–1. Peak torques at 37.5°C were 168 (34), 145 (29), and 112 (17) N m for 60, 120, and 240 s^–1 contraction speeds, respectively, and 166 (38), 150 (31), and 119 (17) N m at T_re of 39.5°C. No significant differences in peak torque at any of the three contraction speeds were observed over the range 37.5–39.5°C. Skin cooling, even with a warm core of 39.5°C, immediately decreased peak torque [159 (42), 133 (34), 107 (22) N m at 60, 120, and 240 s^–1, respectively). We conclude that lowered skin temperature can impair isokinetic force production independent of core temperature.     

The M. omohyoideus of the mouse as a convenient mammalian muscle preparation

Summary Muscles from cats, rats, guinea pigs and mice have been investigated as preparations for visualizing mammalian neuromuscular junctions with the aid of Nomarski interference optics. The M. omohyoideus of the mouse was found to be most convenient. Electrophysiological investigations showed that an endplate is normally surrounded by a population of perijunctional receptors. For junctional receptors in the endplate, a Hill coefficient ofn _H=2.6 for acetylcholine was determined at 38°C, decreasing to a value of 2.3 at room temperature. For both perijunctional and extrajunctional receptors (the latter occurring after denervation), the coefficientn _H was 1.9. Noise analysis revealed a channel conductance which changed abruptly from 22.4±1.0 pS (10–23°C) to 45.6±0.9 pS (34–39°C) in a very small temperature range around 25.5°C. The mean channel lifetime was 0.3 ms at 39°C and 1.0 ms at 23°C.Supported by the Deutsche Forschungsgemeinschaft, SFB 38, N.     

Changes in the index of sweat ion concentration with increasing sweat during passive heat stress in humans

To investigate the pattern changes in the index of sweat ion concentration at skin surface with increasing sweat during passive heat stress in humans, we measured conductivity of the perfused water with sweat as the index of sweat ion concentration and sweat rate, continuously at the chest skin surface. Eight healthy subjects (22.4 ±1.0 years) were passively heated by lower-leg immersion in a hot water bath of 42°C for 50 min in an ambient temperature of 28°C and relative humidity of 50%. The internal temperature (Tor) thresholds of sweat rate and index of sweat ion concentration were almost similar. Concomitant onset for the index of sweat ion concentration and sweat rate occurred but two types of linear regression lines were identified in the relationship between the index of sweat ion concentration and sweat rate at a boundary sweat rate value of 0.30 ± 0.08 mg cm^–2 min^–1. The slope of the regression line at low levels of sweat (slope 0.02 ± 0.01 V mg^–1 cm^–2 min^–1) was significantly gradual compared with that at moderate levels of sweat (slope 0.30 ± 0.08 V mg^–1 cm^–2 min^–1) (P<0.05). These results suggest that at low levels of sweat the index of sweat ion concentration responds gradually with respect to sweat rate, which may be due to the ion reabsorption capacity of the sweat duct, and then the index of sweat ion concentration increased steeply with sweat rate.     

Kinetics of actin monomer exchange at the slow growing ends of actin filaments and their relation to the elongation of filaments shortened by gelsolin

Summary The kinetics of actin monomer exchange with the slow growing pointed ends of actin filaments have been determined by measuring rates of monomer addition to or loss from filaments with their fast-growing barbed ends blocked by the protein gelsolin. Direct measurements of filament length by electron microscopy confirmed that each gelsolin acts as a nucleus for an actin filament. The rate constants ascertained arek _–=0.03s^–1;k ₊=0.06 m ^–1 s^–1 at 23° C andk _–=0.11 s^–1;k ₊=0.09 m ^–1s^–1 at 37° C. They are approximately independent of pH from 7.0 to 8.0 at both temperatures. These rates are far slower than those reported on the basis of some electron microscopic studies of filaments assembled on to actin bundles. The rate constants also predict a higher critical monomer concentration for the pointed end at 37° C than at room temperature, consistent with direct measurements of this quantity. The relative slowness of the monomer exchange at the pointed end suggests that actin filaments with blocked barbed ends are relatively stable. The rate of redistribution of actin monomers from filaments stabilized at their barbed ends by the gelsolin-calcium complex to longer filaments was measured following removal of Ca²⁺, which decreases the capacity of gelsolin to nucleate filaments. The elongation occurs at a rate consistent with the measured rates of monomer exchange and is quantitatively described by Hill's model for filament elongation by random exchange of monomers from one end.     

A slowly inactivating transient outward current in rat ventricular myocytes

In rat ventricular myocytes we found two components of transient outward current, which could be discriminated time- and voltage-dependently. Besides the well known fastly inactivating transient outward current (i_to,f, =35±8ms, n=4) we investigated properties of a slowly inactivating transient outward current (i_to,s, =1.7±0.4s, n=4). Because of the slow inactivation process of i_to,s tail currents were observed at –25mV. The inactivation curve of i_to,f was characterized by a half-inactivation voltage of –58.4±1.4mV and a slope factor of 5.6±0.5mV (n=4). The inactivation curves of i_to,s and tail currents were nearly identical but significantly different from the i_to,f-curve. Half-inactivation voltages of i_to,s and tail currents were –87.5±6mV and –89.1±5mV (n=4), respectively. Slope factors were 10.3±2.9mV and 9.8 ±1.7mV (n=4). The activation gate of i_to,s was half-maximally opened at –11.5±2.6mV, and the slope factor was –10.6±1.7mV (n=3). i_to,s tail current reversed its direction at –62±3.2mV (n=5). This indicates, that i_to,s- current flow is carried mainly by potassium ions. I_to,s- current was not abolished by Tetrodotoxin (TTX) and Cd.     

Ambient temperature and ketone body plasma concentration in fasting geese

The effect on ketonemia of alternate exposure to ambient temperatures (Ta) of 25 and 5°C was investigated in fasting geese. Three experimental birds were compared to three controls continuously exposed to 25°C Ta while fasting. During the first 9 days of fasting, when both groups were exposed to 25°C, plasma concentration of -hydroxybutyrate (-OHB) increased similarly in both, from 0.10±0.02 to 6.62±0.71 mmol·L^–1. It later plateaued at 8–9 mmol·L^–1 in the control birds. When the experimental birds were exposed to 5°C Ta between the 9th and 15th day of the fast, it increased further during the first 24 h but thereafter decreased of 57%, from 8.62±1.56 to 3.73±1.24 mmol·L^–1. This decrease was reversed within the 6 days of return to 25°C Ta. In both groups, plasma acetoacetate (AcAc) concentration remained very low during the fast: 51±1 mol·L^–1. This reversible cold-induced effect on ketonemia may be used for investigating the possible role of ketone bodies in protein sparing during fasting.     

Enhanced glucose availability for working muscles reduces exercise hyperthermia in dogs

Summary Body temperature and metabolic responses to 2 h treadmill exercise in dogs given glucose intravenously (25–30 mg·kg^–1· min^–1 throughout the run) were compared with those measured in the same animals with elevated plasma FFA concentrations (soya bean oil ingestion+intravenous heparin) and in control experiments (24 h fasting). In comparison with control conditions enhanced glucose availability for the working muscles caused a reduction in the exercise-induced increases in both rectal (by 0.9± 0.11° C) and muscle (by 0.9±0.16° C) temperatures, a lower rate of oxygen uptake (by 16%) and an elevated respiratory exchange ratio. A tendency towards enhanced body temperature responses to exercise, accompanied by increases inV _{O 2} and cardiac frequency was noted in dogs with elevated plasma FFA concentrations as compared with the control animals. The estimated amount of heat effectively dissipated from the body, expressed as a fraction of heat load (thermoregulatory efficiency) was significantly higher in dogs infused with glucose (0.962±0.0035), than in the controls (0.947± 0.0043) and those with elevated plasma FFA concentrations (0.931±0.0029).It is concluded that the increased contribution of carbohydrates to the energy yield during exercise results in a marked attenuation of hyperthermia, associated with a reduced metabolic rate and improved thermoregulatory efficiency.This work was supported by the Polish Academy of Sciences within the Project 10.4.