The Japanese Journal of Physiology
Print ISSN : 0021-521X
Volume 53, Issue 4
Displaying 1-8 of 8 articles from this issue
Regular Papers
  • Shigeki Nomoto
    2003 Volume 53 Issue 4 Pages 253-258
    Published: 2003
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Intravenous (I.V.) injection of 10 μg/kg Escherichia coli lipopolysaccharide (LPS), applied at 13:00, evoked in pigeons a biphasic rise of core temperature (Tcore), so that LPS induced with a latency of 30 min first a decrease of Tcore, and 90 min after LPS, Tcore increased, obtaining maximum values from 18:00 to 20:00. Prostaglandins have been considered to be importantly involved in fevers in mammals. To investigate an involvement of prostaglandins in the cyclic variations of Tcore in birds, pigeons were injected I.V. with either 10 mg/kg indomethacin (INDO) or 100 mg/kg aspirin, or they were treated with intracerebroventricular (i.c.v.) injections of 100 μg/kg INDO at various times before or after LPS. When INDO or aspirin was I.V. injected 30 or 15 min before LPS, it diminished the initial decrease of Tcore by more than 50%, whereas the I.V. injection of these drugs 2 and 4 h after LPS did not affect the febrile rise of Tcore. i.c.v. injections of INDO given either before or after LPS neither influenced the initial drop of Tcore nor the following febrile hyperthermia. Both the I.V. injection of 1 mg/kg prostaglandin E2 (PGE2) and the i.c.v. injection of 1 μg/kg PGE2 lowered Tcore. Our observations suggest that prostaglandins are not involved in the febrile elevation of Tcore in pigeons, but appear to participate in the decrease of Tcore, which shortly follows the I.V. injection of LPS. This initial drop of Tcore following LPS may be caused by a peripheral action of prostaglandins because it was not influenced by the i.c.v. injection of indomethacin.
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  • Héctor Rojas, Magaly Ramos, Alfredo Mijares, Reinaldo DiPolo
    2003 Volume 53 Issue 4 Pages 259-269
    Published: 2003
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Previous studies have shown that in contrast to other neuronal cells, Na+/Ca2+ exchange contributes little to Cai2+ homeostasis in rat cerebellar Purkinje neurons under intracellular perfused conditions and at room temperature [Fierro et al.: J Physiol (Lond) 510: 499–512, 1998]. The purpose of this study was to clarify the role of this transporter in cerebellar Purkinje neurons by using intact cells at nearly physiological body temperature. Using Fluo-3 microfluorometry, we have examined the role of the Na+/Ca2+ exchange in the buffering of calcium loads in cultured rat Purkinje neurons at two temperatures: 20 and 34°C. At 20°C, the recovery of the K+-induced [Ca2+]i signal was little affected by the presence of external Na+e = 35.5 ± 1.2 s [n = 49]), or by its absence (τe = 36.6 ± 2.2 s [n = 29]), i.e. in a Li+-containing medium. In contrast, at 34°C, the recovery of the [Ca2+]i signal was highly dependent on external Na, i.e. τe = 19.9 ± 1.2 s (n = 119) and τe = 41.7 ± 2.6 s (n = 39), in Li+-containing media, respectively. A comparison of the rate of clearance of [Ca2+]i in Na+ or Li+ media, shows that at a room temperature of 20°C, the Na+/Ca2+ exchange contributes at most to 15–20% of the total [Ca2+]i clearance, compared to 55–65% at 34–36°C. We also demonstrate that under normal physiological conditions forward and reverse Na+/Ca2+ exchanges operate in the same neuron. We conclude that the Na+/Ca2+ exchange is strongly suppressed at room temperature and therefore its role should be reevaluated among different neuronal preparations.
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  • Bernard Korzeniewski, Jerzy A. Zoladz
    2003 Volume 53 Issue 4 Pages 271-280
    Published: 2003
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    At low power output exercise (below lactate threshold), the oxygen uptake increases linearly with power output, but at high power output exercise (above lactate threshold) some additional oxygen consumption causes a non-linearity in the overall VO2 (oxygen uptake rate)–power output relationship. The functional significance of this phenomenon for human exercise tolerance is very important, but the mechanisms underlying it remain unknown. In the present work, a computer model of oxidative phosphorylation in intact skeletal muscle developed previously is used to examine the background of this relationship in different modes of exercise. Our simulations demonstrate that the non-linearity in the VO2–power output relationship and the difference in the magnitude of this non-linearity between incremental exercise mode and square-wave exercise mode (constant power output exercise) can be generated by introducing into the model some hypothetical factor F (group of associated factors) that accumulate(s) in time during exercise. The performed computer simulations, based on this assumption, give proper time courses of changes in VO2 and [PCr] after an onset of work of different intensities, including the slow component in VO2, well matching the experimental results. Moreover, if it is assumed that the exercise terminates because of fatigue when the amount/intensity of F exceed some threshold value, the model allows the generation of a proper shape of the well-known power-duration curve. This fact suggests that the phenomenon of the non-linarity of the VO2–power output relationship and the magnitude of this non-linearity in different modes of exercise is determined by some factor(s) responsible for muscle fatigue.
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  • Yasuharu Oishi, Kohachi Taniguchi, Hisahiro Matsumoto, Fuminori Kawano ...
    2003 Volume 53 Issue 4 Pages 281-286
    Published: 2003
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    To clarify the changes of heat shock protein (HSP) 72 in the rat soleus muscle after hind-limb unloading (HU) and during reloading, 7-week-old male Wistar rats were hind-limb–suspended for 9 weeks, thereafter ambulatory recovery was permitted for 8 weeks. The body and absolute soleus weights were significantly lower in the HU than in the age-matched control group after HU and during reloading. The soleus weight relative to body weight was also significantly lower in the HU than in the age-matched control group at the end of 9 weeks of suspension, but returned to the control level after 2 weeks of reloading. The HSP72 content decreased to 38% of the control level after HU and conversely increased to 165 and 175% of the control level after 2 and 4 weeks of reloading, respectively. The HSP72 content returned to the control level after 8 weeks of reloading. Thus our results showed that the expression of HSP72 was downregulated by HU and upregulated temporally over the level of the control during the reloading period, and they suggested that these down- and up-regulations of HSP72 may be related to many factors including mechanical stress or load applied to the muscle.
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  • Kazuyoshi Kawa
    2003 Volume 53 Issue 4 Pages 287-299
    Published: 2003
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    The effect of thrombopoietin (TPO), a magakaryocytopoietic cytokine, on the functional maturation of megakaryocytes was studied by using cell culture and patch-clamp techniques focusing on purinergic 2X1 (P2X1)-receptors, which are expressed specifically on platelets and their progenitors. Meg-01 cells, one of the typical human megakaryocytic cell lines, were cultured and studied by using a whole-cell patch electrode. In control cells cultured in RPMI1640 medium, an application of adenosine nucleotide (ADP, 40 μM) evoked transient inward currents with amplitudes of 45 ± 19 pA (at −43 mV). Based on kinetic, ionic, and pharmacological properties as well as on previously reported findings, these currents were thought to be mediated by P2X1 receptors. When Meg-01 cells were cultured for 7−9 d in a medium to which the differentiation-inducing agent phorbol ester (PMA; 10 nM) or TPO (100 ng/ml) had been added, the responses of the cells to ADP increased to about 150% of the control with PMA and to about 200% of the control value with TPO. A combination of the two agents enhanced the response of the cells to ADP to about 570% of the control value. These results suggest that phorbol ester and TPO cause cellular differentiation of Meg-01 cells and enhance the level of expression of P2X1-receptors on cell membranes in a synergetic manner. The effect of TPO on the induction of P2X1-receptors on mouse megakaryocytes in culture was more obvious.
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  • Beata Sokołowska, Adam Jóźwik, Mieczysław ...
    2003 Volume 53 Issue 4 Pages 301-307
    Published: 2003
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    We applied the fuzzy "k-nearest neighbor" (k-NN) classifier of the pattern recognition theory to fathom the abnormal way of breathing resulting from diaphragm paralysis and to distinguish the dominant component, tidal or frequency, of the breathing pattern on which ventilatory compensation relies in such a pathological state. We addressed this issue in the experimental model of diaphragm paralysis as a result of bilateral phrenicotomy in anesthetized, spontaneously breathing cats. Of several variables recorded, we selected two features, minute ventilation and arterial CO2 tension, that were used for the k-NN analysis. The results demonstrate that the ability to maintain ventilation critically depended on the increase in frequency of breathing. Other breathing pattern strategies were ineffective. The k-NN evaluation with the two selected features discerned the prevailing pattern of breathing with sufficient probability. Such an evaluation may be a useful tool in predicting the development of compensatory strategies in disordered patterns of breathing.
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Short Communications
  • Hideto Tanaka, Mikinobu Yasumatsu, Hiroshi Hasegawa
    2003 Volume 53 Issue 4 Pages 309-312
    Published: 2003
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    To clarify the mechanism of body temperature (Tb) rise following voluntary wheel-run training in rats, we investigated the behavioral thermoregulation in female rats by means of a thermal gradient system. We performed thermal gradient tests before training, 4 weeks after training started, and 2 weeks after it stopped. We also examined the effects on the selected ambient temperature and Tb with quantitative training activity. Nine female rats ran voluntarily in a wheel in the range of 6,545 from 1,665 revolutions/night. The higher the wheel-running activity, the higher the Tb level rose at rest during the daytime after 4 weeks of training. The higher-activity rats selected a higher ambient temperature after the training than before, and the Tb was maintained at a high level under this environment. Our results suggest that the rise in Tb level during rest following the wheel-run training is a regulated body temperature change.
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  • Juichiro Shimizu, Satoshi Mohri, Gentaro Iribe, Yutaka Kitagawa, Haruo ...
    2003 Volume 53 Issue 4 Pages 313-318
    Published: 2003
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    We have reported that the postextrasystolic (PES) potentiation of left ventricular (LV) contractility usually decays in alternans at heart rates above 80–100 beats/min in the canine excised, cross-circulated heart. We examined whether the PES contractility would also decay in alternans even in the canine in situ heart presumably more physiological than the excised heart. In anesthetized, ventilated, and open-chest mongrel dogs, we measured LV pressure and volume with a micromanometer and a conductance catheter cannulated into the LV and obtained LV end-systolic maximum elastance (Emax) as the reasonably load-independent contractility index. We inserted an extrasystole followed by a compensatory pause into steady-state regular beats at heart rates above 90 beats/min and analyzed the PES decay pattern of Emax. We found that Emax potentiated in the first PES beat decayed in alternans within 5–6 PES beats. This indicates that PES contractility also decays in alternans in the normal canine in situ heart.
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