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Volume 51 (2001)
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- Issue 2 Pages 133-
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Volume 51, Issue 2
Displaying 1-14 of 14 articles from this issue
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Regular Papers
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Alejandro Lucía, Jesús Hoyos, Javier Pardo, José ...2001 Volume 51 Issue 2 Pages 133-141
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSThe aim of this longitudinal study was to clarify the changes induced by endurance training on the breathing pattern of 13 professional cyclists (age±SD: 24±2 years; V˙O2max~75 ml kg−1 min−1) during the three periods (rest, precompetition, and competition) of a sports season. Both the volume and the intensity of training were quantified during these periods. In each session (corresponding to each of the three periods) all subjects performed (1) a pulmonary function test (to measure forced vital capacity [FVC], peak expiratory flow [PEF], and maximal voluntary ventilation [MVV]), and (2) a ramp test until exhaustion on a cycle ergometer (workload increases of 25 W min−1). The following variables were recorded every 100 W until the end of the tests: pulmonary ventilation (V˙E, in l min−1 BTPS), tidal volume (VT, inl BTPS), breathing frequency (fb, in breaths min−1), ventilatory equivalents for oxygen (V˙E V˙O2−1) and carbon dioxide (V˙E V˙CO2−1), inspiratory (TI) and expiratory (TE) times (s), ratio of TI to total respiratory duration or inspiratory "duty cycle" (TI/TTOT), and mean inspiratory flow rate (VT/TI, in l s−1). The results showed no changes in any of these variables (p>0.05) between the three periods of study, despite significant changes in training loads (i.e., increases in the volume and/or intensity of training throughout the season). These findings suggest that endurance conditioning does not alter the breathing pattern of professional cyclists during an incremental exercise test.
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Gentaro Iribe, Junichi Araki, Satoshi Mohri, Juichiro Shimizu, Takeshi ...2001 Volume 51 Issue 2 Pages 143-149
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSIn our previous studies, we calculated the internal Ca2+ recirculation fraction (RF) after obtaining the beat decay constant (τe) of the monoexponential component in the postextrasystolic potentiation (PESP) of the alternans decay by curve fitting. However, this method sometimes suffers from the sensitive variation of τe with small noises in the measured contractilities of the 5th and 6th postextrasystolic (PES) beats in the tail of the exponential component. We now succeeded in preventing this problem by a new method to calculate RF without obtaining τe. The equation for the calculation in the new method expresses an alternans decay of PESP as a recurrence formula of PESP. It can calculate RF directly from the contractilities of the 1st through the 4th PES beats without any fitting procedure. To evaluate the reliability of the new method, we calculated RF from the alternans decay of PESP of the left ventricle (LV) of the canine excised cross-circulated heart preparation by both the original fitting and the new method. Although there was no significant difference in the mean value of the obtained RF between these two methods, the variance of RF was smaller with the new method than with the original method. Thus the new method proved useful and more reliable than the original fitting method.
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Hisashi Mitsufuji, Hirosuke Kobayashi, Takao Imasaki, Takafumi Ichikaw ...2001 Volume 51 Issue 2 Pages 151-157
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSIn previous studies the exhaled nitric oxide (NO) level of asthma patients was investigated only in association with bronchial inflammation, and whether the degree of bronchoconstriction itself influences the exhaled NO level has never been investigated. We therefore evaluated the effect of inhalation of a bronchoconstrictor (methacholine) or a bronchodilator (salbu-tamol) on the exhaled NO level of healthy volunteers and asthma patients. The exhaled NO level of the healthy volunteers decreased after methacholine inhalation. The exhaled NO level of patients with mild or moderate persistent asthma, who had no asthma attacks on the day of measurement, increased after salbutamol inhalation, and the exhaled NO level of asthma patients during asthma attacks increased after salbutamol inhalation followed by intravenous drip infusion of aminophylline. It is suspected that large amounts of NO are trapped in the lung distal to the constricted airway, contributing little to the exhaled NO level at the mouth. However, we expect that the trapped NO is exhaled at a larger fraction after the dilatation of the constricted small airway, thereby increasing the exhaled NO level at the mouth. In conclusion, the results of this study suggest that acute changes in bronchoconstriction themselves influence the exhaled NO level independently of the change in NO synthase activity associated with airway inflammation.
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Naoki Nagai, Kazuo Kuwata, Tomoya Hayashi, Hiromi Kuwata, Seiichi Era2001 Volume 51 Issue 2 Pages 159-168
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSFourier transform analysis was applied to elucidate the periodical and self-similar properties in the DNA sequences mainly of β-globin genes in different species, and the evolutionary change in those properties was then investigated. Map patterns of a two-dimensional DNA walk showed that the stretches of exons are significantly shorter than those of introns, suggesting that the evolution of exons is driven by natural selection, whereas that of introns is generated by unknown internal rules. Using a monomer analysis, we obtained the power spectra of four different bases, A, G, C, and T, in DNA sequences. Periodicities in the short- (2 to 10 base pairs [bp]), medium- (10 to 50 bp) and long-range order (50 to 300 bp) of β-globin gene sequences could be observed, and power spectral densities of these periodicities were increased with evolution. These results suggest the existence of the internal rules in the occurrence of the synonymous and nonsynonymous substitutions in the sequences, the destabilization of the interaction between DNA and histone protein, and the stabilization of the chromatin structure, respectively. Moreover, 1/fα analysis of the power spectra (log-log plot) in the far long-range region (160 to 16,000 bp) suggested the increase in the self-similarity (the fractal structure) of DNA sequences with evolution. A general trend of the increase in a 3 bp periodicity with evolution might be functionally related to the CAG trinucleotide repeat diseases such as Huntington chorea, where a marked periodicity of 3 bp could be observed. Fourier transform analysis applied to a DNA sequence offers a great new avenue for extracting information on the evolution of a DNA sequence.
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Tsukasa Tameyasu, Mitsuyo Shimada, Haruo Sugi2001 Volume 51 Issue 2 Pages 169-176
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSThe effect of external [Ca2+] ([Ca2+]o) on Ca2+ release from the sarcoplasmic reticulum (SR) was examined with rested-state twitches in rat ventricular myocytes. The magnitude of transient rise of intracellular [Ca2+] ([Ca2+]i) relative to the resting one, F/Fo, as measured with fluo-3, was 1.75±0.07 (mean±SEM, n=9) and 1.86±0.13 (n=9) at 0.3 and 1.8 mM [Ca2+]o, respectively; the difference was insignificant. The time from onset to peak and the rate of rise of the [Ca2+]i transient were 0.107±0.017 s (n=9) and 18.8±3.38 F/Fo/s, respectively, at 0.3 mM [Ca2+]o, they were 0.064±0.005 s (n=9) and 31.1±0.03 F/Fo/s, respectively, at 1.8 mM [Ca2+]o. The difference in the corresponding values at the two [Ca2+]o was significant (t-test, p<0.05). The half decay time of the [Ca2+]i transient was 0.217±0.016 s (n=8) at 0.3 mM [Ca2+]o and was similar to the value of 0.230±0.022 s (n=8) at 1.8 mM [Ca2+]o, indicating that the rate of decrease of [Ca2+]i is independent of the [Ca2+]o. The duration of action potential was similar at 0.3 and 1.8 mM [Ca2+]o as examined with papillary muscle. The results suggest that a lowering of [Ca2+]o, i.e., reducing the Ca2+ influx, slows the rate of Ca2+ release from the SR fully loaded with Ca2+ with little effect on the total amount of the Ca2+ release. An instantaneous relationship between the [Ca2+]i and the myocyte shortening at 0.3 and 1.8 mM [Ca2+]o suggested that the time course of unloaded contraction is related not only to the magnitude, but also to the rate of rise of [Ca2+]i.
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Susumu Sakata, Yoshimi Ohga, Takehisa Abe, Nobuoki Tabayashi, Shuichi ...2001 Volume 51 Issue 2 Pages 177-185
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSWe have reported the linear relation of myocardial oxygen consumption per beat (VO2) and systolic pressure-volume area (PVA) in the left ventricle of the cross-circulated rat heart. The VO2 intercept (PVA-independent VO2) is primarily composed of VO2 for Ca2+ handling in excitation-contraction coupling and basal metabolism. Recently, we proposed a new index for oxygen cost of contractility obtainable as a slope of a linear relation between PVA-independent VO2 and left ventricular contractility. This index indicates the Ca2+ handling VO2 per unit contractility change. However, a dependency of this index on heart rate has not yet been investigated. The aim of the present study was to investigate the dependency of oxygen cost of contractility on heart rate. This is a critical point to compare this cost under different heart rates. At first we found no differences of VO2-PVA relations at 240 and 300 beats/min (bpm). Therefore, after control VO2-PVA relation at 300 bpm, we gradually enhanced left ventricular contractility by Ca2+ at a midrange left ventricular volume and obtained the gradually increased PVA-independent VO2. At each contractility level, the pacing rate was alternately changed at 240 and 300 bpm. We obtained the two composite VO2-PVA relation lines and found no significant differences between the slopes of PVA-independent VO2 and left ventricular contractility relations at 240 and 300 bpm. The present results indicated no dependency of oxygen cost of left ventricular contractility on heart rates within 240-300 bpm. Based on this fact, we concluded that even under the different pacing rates within 240-300 bpm, this oxygen cost is valid for assessing cardiac mechanoenergetics, especially the economy of total Ca2+ handling in E-C coupling.
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Tsukasa Tameyasu, Mitsuyo Shimada, Haruo Sugi2001 Volume 51 Issue 2 Pages 187-191
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSCa2+ release from the sarcoplasmic reticulum (SR) in heart muscle grades depending on Ca2+ influx in the physiological twitch; Ca2+ wave results from regenerative Ca2+ release from the SR. To examine if the Ca2+ release from the SR in the Ca2+ wave takes a duration similar to the physiological one, a transient rise of intracellular [Ca2+] ([Ca2+]i transient) was recorded during both a propagating Ca2+ wave and an electrically evoked twitch with single rat ventricular myocytes, using a laser scanning confocal microscope. Care was taken to record the fluo-3 fluorescence from a segmental region with little lateral movement, especially during a propagating Ca2+ wave. During a typical Ca2+ wave, the time-to-peak (TP) and the half-width (HD) of the averaged [Ca2+]i transient were 161 and 253 ms respectively, but they were 76 and 145 ms during an electrically evoked twitch. The difference in the duration between the two types of [Ca2+]i transients could not be accounted for by modification of duration of [Ca2+]i transient by possible asynchronous Ca2+ release from the SR during a Ca2+ wave, suggesting that the regenerative Ca2+ release from the SR in the Ca2+ wave occurs more slowly than the physiological one in rat ventricular myocytes.
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Junichi Take, Takeo Yamaguchi, Naoki Mine, Shigeyuki Terada2001 Volume 51 Issue 2 Pages 193-199
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSMurine erythroleukemia cells were subjected to physicochemical stresses such as high pressure (60-110 MPa), heating (42-45°C), and ultraviolet (UV) irradiation (5-25 kJ/cm2). After exposure to these stresses, the cells were cultured at 37°C and atmospheric pressure. The number of the cells treated at 100 MPa, 45°C, or 20 kJ/cm2 remained constant or decreased at an early stage of culture. The nuclear morphology, agarose gel electrophoresis, and flow cytometry of these cells showed that they undergo apoptosis. The activity of caspase-3 was observed in cells subjected to each stress. In particular, caspase-3 was most readily activated by high pressure under our conditions. The caspase-3 activity and apoptosis exhibited a similar pressure dependence. It is important that both caspase-3 activation and apoptosis induced by high pressure were significantly suppressed by a caspase-3 inhibitor. These results suggest that high-pressure-induced apoptosis is also characterized by the activation of caspase-3, as seen with heat- and UV-induced apoptosis.
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Roumiana Bakalova, Tetsuya Matsuura, Iwao Kanno2001 Volume 51 Issue 2 Pages 201-208
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSWe measured the field potential and the changes in local cerebral blood flow (LCBF) response during somatosensory activation (evoked LCBF) in α-chloralose-anesthetized rats by laser-Doppler flowmetry under normocapnia (PaCO2=34.3±3.8 mmHg) and hypercapnia (PaCO2=70.1±9.8 mmHg). Somatosensory activation was induced by electrical stimulation (0.2, 1, and 5 Hz with 1.5 mA for 5 s) of the hind paw. The neuronal activity of the somatosensory area of the hind paw was linear to the stimulus frequency, and there was no significant difference in the neuronal activity between hypercapnia and normocapnia. The baseline level of LCBF under hypercapnia was about 72.2% higher than that under normocapnia (p<0.01). The absolute response magnitude under hypercapnia was greater than that under normocapnia (p<0.05). The evoked LCBF under both conditions showed a frequency-dependent increase in the 0.2 to 5 Hz range, and the difference in the absolute response magnitude at the same stimulus frequency between normocapnia and hypercapnia became large with increasing stimulus frequency (p<0.05). On the other hand, after normalization to each baseline level there was no significant difference in the response magnitude of the normalized evoked LCBF between normocapnia and hypercapnia, indicating that the normalized evoked LCBF reflects neuronal activity even when the baseline LCBF was changed by the PaCO2 level. The peak time and termination time of LCBF response curves with respect to the graded neuronal activity at 1 and 5 Hz stimulation increased significantly under hypercapnia, compared with those under normocapnia (p<0.05), although the rise time of 0.5 s was nearly constant. In conclusion, the results suggest a synergistic effect of the combined application of graded neuronal stimuli and hypercapnia on the LCBF response.
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Keigo Ueda, Yasuaki Aoyama, Fumiyo Sasaka-Kitamura, Yasuaki Kawai2001 Volume 51 Issue 2 Pages 209-215
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSIn the present study, the effects of head-down tilt (HDT) on contractile responses of basilar and popliteal arteries were investigated in vitro. The arteries were isolated from rabbits exposed to 8 d of 45° HDT. Isometric tension and intracellular calcium were measured in an organ bath perfused with physiological salt solution. In the HDT rabbits, contractile response to norepinephrine (NE) was attenuated in the basilar artery, but not in the popliteal artery compared with control rabbits. HDT did not change the responses to either KCl or 5-hydroxytryptamine in both arteries. In the response of basilar artery to NE, the difference in both [Ca2+]i transient and Ca sensitivity between control and HDT rabbits were statistically not significant. The response of the basilar artery to phenylephrine, a selective α1-adrenergic agonist, was also attenuated by HDT. Treatment with propranolol, a β-adrenergic blockade, did not affect the response to NE in the basilar arteries isolated from control rabbits, but it significantly enhanced the response in the basilar arteries from HDT rabbits. These results suggest that exposure to 8-d HDT decreases a contractile response of the basilar artery to NE in rabbits. The reduction of NE-induced contraction is probably attributable to both decreased Ca transient and decreased Ca sensitivity, and decreased α1-adrenoceptor activity and increased β-adrenoceptor activity seem to be involved in the mechanism.
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A New Model-Based Method of Reconstructing Central Aortic Pressure from Peripheral Arterial PressureMasaru Sugimachi, Toshiaki Shishido, Kunio Miyatake, Kenji Sunagawa2001 Volume 51 Issue 2 Pages 217-222
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSWe have shown in our previous study that the transfer function between central aortic pressure and tonometric radial arterial pressure can be modeled as a pure elastic lossless tube terminated with a modified Windkessel. We hypothesized, using the model-derived radial arterial flow, that central pressure could be reconstructed by adding the time-shifted forward and backward pressure components (Stergiopulos et al.: Am J Physiol 274: H1386-H1392, 1998). In eight patients (age 16-75), central micromanometric and radial arterial tonometric pressure were measured simultaneously. We imposed measured tonometric pressure to the terminal modified Windkessel to estimate radial arterial flow, with which tonometric pressure was separated into forward and backward components. These components were then appropriately time shifted, and summed to central pressure. We used average parameter values for the terminal impedance, but individualized the transmission delay. The poor correlation (r2) between tonometric and central pressure (0.264-0.765) was improved by both central pressure reconstruction methods (generalized transfer function: 0.887-0.974, model-based method: 0.849-0.979). The sensitivity analysis indicated that the key model parameter in reconstructing central pressure was the transmission delay. We conclude that our model-based method was capable of reconstructing central pressure as precisely as the generalized transfer function method, and also capable of individualizing the transfer function by changing the transmission delay.
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Lin Piao, Ying Li, Lin Li, Nan Ge Jin, Zai Liu Li, Wen Xie Xu2001 Volume 51 Issue 2 Pages 223-230
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSIn our study of the effects of hyposmotic swelling on the Ca2+-activated potassium currents [IK(Ca)] and its mechanism, we employed the whole-cell patch clamp technique using the gastric antral circular myocytes of the guinea-pig. Hyposmotic swelling efficiently increased IK(Ca), and the extent of changes in IK(Ca) was sharply dependent on the osmolarity of the perfusion solutions. When the calcium-free solution (EGTA 10 μM added in calcium-free solution) was superfused, IK(Ca) was not increased by the hyposmotic swelling. Gadolinium (Gd3+) 100 nM, a blocker of the stretch-activated nonselective cation channel, blocked the activation of IK(Ca) induced by hyposmotic swelling, but nicardipine 5 μM (the L-type calcium channel blocker) did not. Heparin 3 mg/ml, a potent inhibitor of inositol triphosphate receptor (InsP3R), did not inhibit the response, and caffeine 1 mM (the agonist for calcium-induced calcium release [CICR]) imitated the effect of hyposmotic swelling. Ryanodine (15 μM), markedly inhibited the effect. These results suggest that hyposmotic swelling activates IK(Ca), and the activation is associated with CICR, which is triggered by extracellular calcium influx through the stretch-activated channel (SA channel).
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Yi Syuu, Hiromi Matsubara, Takahiko Kiyooka, Shingo Hosogi, Satoshi Mo ...2001 Volume 51 Issue 2 Pages 231-238
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSNeiguan (PC-6) is a traditional acupoint in the bilateral forearms, overlying the median nerve trunk. Neiguan electroacupuncture (EA) has been believed to affect cardiovascular function and used in traditional Chinese medicine to improve or treat a wide range of health conditions and diseases, including angina pectoris, myocardial infarction, hypertension, and hypotension. However, few physiological studies have assessed the beneficial effects of Neiguan EA on the cardiovascular function. In the present study, we investigated its effects on the cardiovascular function in normal open-chest dogs under pentobarbital and fentanyl anesthesia. We also obtained left ventricular (LV) pressure-volume (P-V) data with a micromanometer catheter and a volumetric conductance catheter. Mean arterial pressure, end-diastolic volume, heart rate, stroke volume, cardiac output, and end-systolic pressure gradually decreased by 5 to 10% over 1.5 h without Neiguan EA. Neiguan EA at 40 Hz, however, increased these cardiovascular variables by 10 to 15%, especially end-systolic elastance (Ees) by 40% (p<0.05) over 15 to 60 min. After Neiguan EA was stopped at 1 h, these facilitated cardiovascular variables decreased below the pre-EA level. This beneficial effect of electroacupuncture may contribute to the effectiveness of the acupuncture in Chinese medicine.
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Short Communication
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Alejandro Lucía, Jesús Hoyos, Margarita Pérez, Jo ...2001 Volume 51 Issue 2 Pages 239-242
Published: 2001
Released on J-STAGE: June 19, 2004
JOURNAL FREE ACCESSWe analyzed the relationship between the plasma concentrations of several hormones (testosterone [T], follicle-stimulating [FSH] and luteinizing hormone [LH], cortisol [C], 3,5,3′-triiodothyronine [T3], thyroxine [T4], and thyrotrophin [TSH]) and the magnitude of the V˙O2 slow component (δV˙O2) in a group of nine professional road cyclists (26±2 years). The resting levels of the aforementioned hormones were determined before the subjects performed a 20-min cycle ergometer test at ~80% of V˙O2 max (or ~400 W). Plasma concentrations of T3 and T4 were inversely correlated (p<0.05) with δV˙O2 (r=−0.72 and r=−0.66, respectively), suggesting, at least partly, and association between thyroid basal function and the V˙O2 slow component of euthyroid elite endurance athletes during constant-load intense exercise.
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