The Japanese Journal of Physiology
Print ISSN : 0021-521X
Volume 52, Issue 1
Displaying 1-14 of 14 articles from this issue
REVEIW
  • Kenichi Matsunami
    2002 Volume 52 Issue 1 Pages 1-20
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Studies of the vestibular system in squirrel monkeys in consideration of space motion sickness (SMS) or space adaptation syndrome (SAS) were reviewed. First, the phylogenetic position of the squirrel monkey was considered. Then the anatomico-physiological studies of both the peripheral and the central vestibular systems were described, because the vestibular system is crucially important in the genesis of SMS (SAS). In this connection, the ablation studies of labyrinth, semicircular canals, and other SAS-related areas were referred to, and consideration was made for experiments about caloric irrigation of the ear. A hypothetic model was then proposed for the genesis of SAS.
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Regular Papers
  • Toru Kawada, Toshiaki Shishido, Masashi Inagaki, Can Zheng, Yusuke Yan ...
    2002 Volume 52 Issue 1 Pages 21-29
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Two types of closed-loop perturbations can be applied to the arterial baroreflex system. The first (PD1) is introduced into the baroreceptors without a direct effect on arterial pressure (AP), whereas the second (PD2) initially affects AP. Neck suction and hemorrhage are examples of PD1 and PD2, respectively. To estimate the baroreflex open-loop gain (GBaro) without knowing the absolute magnitudes of PD1 and PD2, we explored a new strategy to estimate GBaro by combining PD1 and PD2 in a baroreflex equilibrium diagram. In this diagram, the neural arc presents the input-output relationship between baroreceptor pressure input and sympathetic nerve activity (SNA). The peripheral arc presents the input-output relationship between SNA and AP. In 8 anesthetized rabbits, we estimated GBaro by multiplying the slopes of the peripheral arc determined from PD1 and the neural arc determined from PD2. We also estimated GBaro by a conventional open-loop analysis. The GBaro values estimated by the equilibrium diagram and the open-loop analysis showed a positive correlation (y = 0.80x + 0.22, r2 = 0.95) and a standard error of estimate of 0.21 across the animals. We conclude that GBaro was estimated well by combining PD1 and PD2 in the equilibrium diagram.
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  • Tomoyuki Kubota, Minoru Horie, Makoto Takano, Hidetada Yoshida, Hideo ...
    2002 Volume 52 Issue 1 Pages 31-39
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Cell swelling enhances a slowly activating delayed rectifier K+ current (IKs) in cardiac cells. This investigation was undertaken to determine which of the two structural units reconstituting the IKs channel, KCNQ1 (KvLQT1) and KCNE1 (minK/IsK), plays a key role in the cell swelling-induced IKs enhancement and to dissect a possible involvement of tyrosine phosphorylation therein. KCNQ1 was transiently expressed alone or together with KCNE1 in a heterologous mammalian cell line. Two distinct whole-cell membrane currents were separately observed during the exposure of transfected cells to various degrees of hyposmotic solutions. A hyposmotic challenge (0.7 times control osmolarity) resulted in about a twofold increase not only in the heteromeric KCNQ1/KCNE1, but also in the homomeric KCNQ1 channel currents. There was no significant difference in the incremental ratio of current amplitude in response to hyposmotic stress between the two KCNQ1-related currents, and the cells expressing the heteromeric channels swelled less than those with the homomeric channels or without the exogenous ones. The cell swelling-induced IKs enhancement was not affected by a protein tyrosine kinase (PTK) inhibitor, by genistein (50 μM), or by an inhibitor of phosphotyrosine phosphatase (PTP), orthovanadate (500 μM), or a nonhydrolyzable ATP analogue, AMP-PNP (5 mM). Taken together, it is very likely that KCNQ1 might primarily participate in the IKs enhancement by osmotic cell swelling. The obligatory dependence of the IKs augmentation on PTK activity remained to be demonstrated, at least, in this expression system.
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  • Terumasa Morita, Junichi Araki, Yu Oshima, Hidenobu Mitani, Gentaro Ir ...
    2002 Volume 52 Issue 1 Pages 41-49
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Mean levels of left ventricular rhythm and contractility averaged over arrhythmic beats would characterize the average cardiac performance during atrial fibrillation (AF). However, no consensus exists on the minimal number of beats for their reliable mean values. We analyzed their basic statistics to find out such a minimal beat number in canine hearts. We produced AF by electrically stimulating the atrium and measured left ventricular arrhythmic beat interval (RR) and peak isovolumic pressure (LVP). From these, we calculated instantaneous heart rate (HR = 60,000/RR), contractility (Emax = LVP/isovolumic volume above unstressed volume), and beat interval ratio (RR1/RR2). We found that all their frequency distributions during AF were variably nonnormal with skewness and kurtosis. Their means ± standard deviations alone cannot represent their nonnormal distributions. A 90% reduction of variances of Emax and RR1/RR2 required a moving average of 15 and 24, respectively, arrhythmic beats on the average, whereas that of RR and HR required 60 beats on the average. These results indicate that a statistical characterization of arrhythmic cardiodynamic vari-ables facilitates better understanding of cardiac performance during AF.
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  • Jianguo Zhuang, Haifeng Zhu, Zhaonian Zhou
    2002 Volume 52 Issue 1 Pages 51-56
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Tibetans are known as one of the largest and oldest high-altitude natives in the world and are among the best high-altitude-adapted ethnic groups. They exhibit greater vagal tone and less sympathetic stimulation than acclimatized lowlanders at high altitudes. Whether young native Tibetans who had spent long-term residence (more than 3 years) at sea level still reserved their unique autonomic characteristics was the main aim of this study. Heart rate variability (HRV) of 10 native young Tibetan male students and 12 Han counterparts were measured at resting supine position at sea level and 1 h after ascent to 3,700 m in a hypobaric chamber (PO2 = 13.4 kPa). At sea level, Tibetans showed lower heart rate (HR) and greater HRV. At 3,700 m, the increase of HR was greater in the Hans than in the Tibetans, and the HRV was significantly diminished in the Han group but not in the Tibetan group. The results suggested that Tibetans had a greater parasympathetic dominance over the heart at rest, and acute mod-erate (3,700 m) hypoxia did not influence their HRV significantly, but it did on the Han subjects. We concluded that the long-term residence of the Tibetans at sea level did not change their unique characteristics of the autonomic systems.
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  • Tsukasa Tameyasu
    2002 Volume 52 Issue 1 Pages 57-68
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    To elucidate the essential features of Ca2+ release from the terminal sac (TS) of the sarcoplasmic reticulum (SR) in heart muscle, a model for Ca2+ release from the TS was constructed based on the mechanism of Ca2+-induced Ca2+-release by assuming a small TS volume. For numerical computation, we divided the cytoplasm in a half sarcomere into 50 compartments, one end of which faced the TS and determined the open probability of the Ca2+ release channel in the TS. Ca2+ moves from compartment to compartment by simple diffusion and is taken up from each compartment by the tubular SR via Ca2+-ATPase. Simulation based on one-dimensional diffusion of Ca2+ showed that TS Ca2+ release is smoothly graded over a wide range of levels of Ca2+ influx when the TS is moderately loaded with Ca2+, and it occurs in an all-or-none manner when the TS is heavily loaded with Ca2+. The graded TS Ca2+ release was generated with both local and uniform Ca2+ influx into the cytoplasm. The propagation of the Ca2+ wave was simulated by the use of a model consisting of several longitudinally consecutive sarcomeres with TS heavily loaded with Ca2+. Mechanical alternans, characterized by an alternation of small and large twitches, was also simulated by applying Ca2+ influx at an appropriate interval during which Ca2+ was replenished to the TS at a constant rate. Thus the present model reflects several important aspects of TS Ca2+ release in heart muscle.
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  • Qi Fu, Satoshi Iwase, Yuki Niimi, Astunori Kamiya, Daisaku Michikami, ...
    2002 Volume 52 Issue 1 Pages 69-76
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    The present study was performed to test the hypothesis that calf venous capacitance would be reduced by mild gravitational stress through a vasomotor reflex in humans, and this response could be diminished with advancing age. Nine young (31 ± 1 years, mean ± SE) and 9 elderly (69 ± 1 years) healthy males were exposed to a lower body negative pressure (LBNP) of 15 mmHg. Venous occlusion plethysmography was used to measure calf venous capacitance and calf blood flow. Muscle sympathetic nerve activity (MSNA) was recorded microneurographically from the tibial nerve along with cardiovascular variables. It was found that baseline MSNA was higher [21 ± 4 (mean ± SE) vs. 37 ± 5 bursts·min−1, young vs. elderly; p < 0.05] and calf venous capacitance was lower (1.71 ± 0.12 vs. 1.44 ± 0.10, ml·100 ml−1, young vs. elderly; p < 0.05) in the elderly group. At 15 mmHg-LBNP, heart rate and mean arterial pressure both remained unchanged, MSNA was enhanced, and calf blood flow was reduced in all subjects. Calf venous capacitance during LBNP decreased in the young, but did not change in the elderly. A significant negative correlation between percent changes in MSNA and percent changes in calf venous capacitance existed in the young group (y = 20.171x−11.863, r = 20.682; p = 0.0432), but disappeared in the elderly group. The ratio of percent changes in calf venous capacitance to percent changes in MSNA was markedly lower in the elderly (p < 0.01). In conclusion, these results substantiate our hypothesis that calf venous capacitance is reduced by mild LBNP through the vasomotor reflex, and this response is diminished in the elderly.
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  • Qi Fu, Satoshi Iwase, Yuki Niimi, Atsunori Kamiya, Daisaku Michikami, ...
    2002 Volume 52 Issue 1 Pages 77-84
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    To test the hypothesis that leg vein filling and emptying functions could be impaired with advancing age, which would produce less blood volume redistribution toward the lower body and smaller sympathetic reflex response during mild gravitational stress, 9 young and 10 elderly healthy males were exposed to a lower body negative pressure (LBNP) of 15 mmHg. Venous occlusion plethysmography was used to determine the functions of the leg veins. We found that the baseline venous distensibility index (VDI) was lower (0.057 ± 0.004 vs. 0.048 ± 0.003 ml·100 ml−1·mmHg−1, young vs. elderly; p < 0.05), and half-emptying time (T1/2) was shorter (1.6 ± 0.1 vs. 1.3 ± 0.1 s, young vs. elderly; p < 0.05) in the elderly. At 15 mmHg-LBNP, VDI was decreased and T1/2 was shortened significantly in the young group, but only slightly in the elderly group. Neither blood pressure nor heart rate changed significantly in either group. The reduction in peripheral venous pressure, which was recorded from the left antecubital vein at the cubital fossa, was less in the elderly, indicating a smaller decrease in central blood volume during LBNP; however, the enhancement of muscle sympathetic nerve activity was nearly the same as that in the young. We conclude that leg vein filling and emptying functions are impaired in elderly people, producing less blood pooling in the legs and smaller reduction in peripheral venous pressure during LBNP; the maintained sympathetic reflex response might be attributable to the well-preserved baroreflex function control of sympathetic outflow to the muscle in the elderly.
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  • Takeshi Nomura, Fuminori Kawano, Myung Sun Kang, Jun Hak Lee, Eun Youn ...
    2002 Volume 52 Issue 1 Pages 85-93
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    The effects of 20-week cold exposure on contractile properties of soleus and extensor digitorum longus (EDL) muscles and plasma hormone levels were studied in rats. Twenty male Wistar rats (5 week old) were randomly divided into 2 groups (n = 10 each): cage-control and cold-exposed. The rats in the cold-exposed group were immersed in shoulder-deep water (~18°C) for 1 h/d, 5 d/week, for 20 weeks. The temperature and humidity of the animal room with 12:12 h light-dark cycle were maintained at ~23°C and 55%, respectively. The rats were pair-fed powdered diets. The electromyogram activities in soleus and EDL were elevated by cold exposure. The body weight and absolute soleus wet weight of the cold-exposed group were significantly less than controls at the end of experiment. The one-half relaxation time and contraction time of EDL were significantly longer in the cold-exposed group than in the control group. The rate of twitch tension development, normalized by the maximum twitch tension, in EDL of the cold-exposed group was less than in the control group. Further, the fatigue resistance of EDL, but not of soleus, in response to train stimulation at 10 Hz was improved by cold exposure. The plasma levels of thyroid hormones, 3,5,3′-triiodothyronine and thyroxine, were significantly greater in cold-exposed group. Similar changes were also seen in the plasma catecholamine levels in the cold-exposed group (p > 0.05). It is suggested that long-term cold exposure causes a shift of the contractile properties of fast-twitch EDL muscle toward the slow-twitch type. The results also indicated that the characteristics of muscles responded more strongly to an increased activity level than to the elevation of plasma hormones.
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  • Alejandro Lucía, Jesús Hoyos, Alfredo Santalla, Margarit ...
    2002 Volume 52 Issue 1 Pages 95-103
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    The purpose of this study was to determine (1) if there exists an additional, nonlinear increase (ΔVO2) in the oxygen uptake observed (VO2 obs) at the maximal power output reached during a ramp cycle ergometer test and that expected (VO2 exp) from the linear relationship between VO2 and power output below the lactate threshold (LT) in professional riders, and (2) the relationship between ΔVO2 and possible explanatory mechanisms. Each of 12 professional cyclists (25 ± 1 years; VO2 max: 71.3 ± 1.2 ml·kg−1·min−1) performed a ramp test until exhaustion (power output increases of 25 W·min−1) during which several gas-exchange and blood variables were measured (including lactate, HCO3 and K+). VO2 was linearly related to power output until the LT in all subjects. Afterward, a nonlinear deflection was observed in the VO2:power output relationship (ΔVO2 = 2492 ± 55 ml·min−1 and p < 0.05 for VO2 obs vs. VO2 exp). A significant negative correlation was encountered between ΔVO2 and resting hemoglobin levels before the tests (r = 20.61; p < 0.05). In conclusion, professional cyclists exhibit an attenuation of the VO2 rise above the LT.
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  • Yasumasa Asai, Sadanori Inoue, Kyouko Tatebayashi, Yoshimitsu Shiraish ...
    2002 Volume 52 Issue 1 Pages 105-110
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Changes in cerebral blood flow (CBF) and somatosensory-evoked potentials (SEPs) were studied in rabbits exposed to head-down tilt (HDT) at 45° and 75°. The animals were anesthetized with alpha chloralose and the lungs were artificially ventilated. CBF was continuously measured by laser Doppler flowmetry (LDF), and SEPs were recorded as responses of the cortex to median nerve stimulation. In the 45° HDT rabbits, CBF did not change significantly in the parietal cortex during 1 h of HDT. In contrast, in the 75° HDT rabbits, CBF did not change significantly within 5 min after the onset of HDT, but decreased gradually to 79% of the pre-HDT baseline value at the end of 1 h of HDT. The latency and amplitude of SEPs did not change significantly throughout the experiment in any group. These results suggest that CBF and SEPs do not change significantly during 1 h of 45° HDT and that 75° HDT disturbs the regulation of the cerebral circulation but does not affect cortical somatosensory response, at least for 1 h.
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  • Tsukasa Tameyasu, Megumi Yamada, Midori Tanaka, Saeko Takahashi
    2002 Volume 52 Issue 1 Pages 111-120
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    The effect of antioxidant Z-103, catena-(S)-[μ-[Nα-(3-aminopropinyl)histidinnato-(2-)N1,N2,O:Nτ]-zinc], on muscle function in the muscular dystrophy (mdx) mouse was examined by repetitive intraperitoneal administration in subjects aged 4 to 12 weeks. Z-103 administration at a dose of 150 mg/kg increased the load resistant time (LRT), during which the animal with a load holds itself upright on a wire net. The Z-103 administration reduced hypertrophy, the ratio of centronucleated myofibers, and the rate of decay for magnitude of twitch force elicited by 0.5 Hz of electricity to the extensor digitorum longus (EDL) muscle of 12-week-old mdx mice, with little effect on the magnitude of twitch force. The administration of Z-103 (100 mg/kg) had a lesser effect on LRT and the other characteristics examined for EDL muscles. The constituent of Z-103, Zn2+ applied in the form of ZnSO4 (5 mg/kg), carnosine (100 mg/kg), and the combination of the two had no beneficial effect on mdx mice. Z-103 (150 mg/kg) administered to normal mice increased LRT with little effect on the contractile properties of EDL muscles. These results suggest that the administration of Z-103 ameliorates muscle function in the mdx mouse.
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  • Kenichi Hongo, Yoichiro Kusakari, Makoto Kawai, Masato Konishi, Satosh ...
    2002 Volume 52 Issue 1 Pages 121-127
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    We used the relation between intracellular Ca2+ concentration ([Ca2+]i) and cell shortening during tetanus to evaluate the endogenous characteristics of Ca2+ responsiveness of myofibrils in mouse ventricular myocytes. Enzymatically isolated myocytes were loaded with fura-2 AM (4 μM for 10 min), and the fura-2 fluorescence ratio at 340 and 380 nm excitation wave length [F(340)/F(380)] and cell length were measured simultaneously. Following treatment with thapsigargin (0.2 μM) (an inhibitor of the Ca2+ pump of sarcoplasmic reticulum), myocytes were stimulated at 10 Hz for 10 s to produce a tetanic contraction and an instantaneous plot of the fluorescence ratio signal versus cell length (R-L trajectory) was constructed. An increase in the extracellular Ca2+ concentration ([Ca2+]o) from 0.5 to 2 mM extended the R-L trajectory without a substantial shift of the relation. The R-L trajectory was shifted rightward by the nonselective phosphodiesterase inhibitor, 3-isobutyl-1-methyl-xantine (IBMX, 200 μM) (desensitization of the myofibrils to Ca2+), and shifted leftward by the Ca2+ sensitizing thiadiazinone derivative, EMD-57033 (0.5 μM) (sensitization of the myofibrils to Ca2+). β-Adrenergic stimulant, isoproterenol (5 nM), also shifted the R-L trajectory to the right, suggesting that the membrane receptor could be preserved. These results suggest that the R-L trajectory is a useful method to estimate the myofibrillar responsiveness to Ca2+ in isolated mouse myocytes and can be applied to various mouse models of heart disease.
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Short Communication
  • J. X. Zhu, Y. M. Chan, L. L. Tsang, L. N. Chan, Q. Zhou, C. X. Zhou, H ...
    2002 Volume 52 Issue 1 Pages 129-134
    Published: 2002
    Released on J-STAGE: June 19, 2004
    JOURNAL FREE ACCESS
    Bak Foong Pills (BFP, also known as Bai Feng Wan) is an over-the-counter traditional Chinese medicine that has long been used for treating gynecological disorders and improving overall body functions, including gastrointestinal (GI) function. However, the cellular signaling mechanism underlying BFP action, especially on the GI tract, has not been elucidated. In the present study, the human colonic epithelia cell line T84 was used as a model to investigate the effect of BFP ethanol extract on ion transport in conjunction with the short-circuit current (ISC) technique. The results showed that the apical addition of BFP extract produced a concentration-dependent (10-1,000 μg/ml, EC50 = 120 μg/ml) increase in ISC. The maximal response was observed at 500 μg/ml with an increase in ISC of 24.4 ± 2.3 μA/cm2 and apical conductance. The BFP-induced ISC was not observed when extracellular Cl was replaced or when treated with Bumetanide (100 μM), an inhibitor of the Na+-K+-2Cl cotransporter. The BFP-induced ISC was insensitive to the Na+ channel blocker, amiloride, but partially inhibited by the Cl channel blocker, DIDS (100 μM), and completely blocked by DPC (2 mM) or glibenclamide (1 mM) with a significant reduction in the apical conductance. The BFP-induced ISC could be mimicked by forskolin (10 μM), but inhibited by a pretreatment of the cells with adenylate cyclase inhibitor, MDL-12330A (10 μM). Pretreatment with EGTA (5 mM) and thapsigargin (10 μM) decreased the BFP-induced ISC by 10%. These results demonstrated that BFP ethanol extract exerted a stimulatory effect on gastrointestinal Cl secretion by predominantly activating adenylate cyclase and apical cAMP-dependent Cl channels, with minor contributions from calcium-dependent Cl channels. The effect of BFP may be explored to treat GI disorders such as constipation.
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