The Japanese Journal of Physiology
Print ISSN : 0021-521X
Volume 48, Issue 6
Displaying 1-12 of 12 articles from this issue
Reviews
  • Nobuya INAGAKI, Susumu SEINO
    1998 Volume 48 Issue 6 Pages 397-412
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    ATP-sensitive potassium channels (KATP channels) play important roles in various tissues by coupling cell metabolic status to electrical activity. Recently, molecular biological and electrophysiological techniques have revealed the molecular basis of the KATP channels to be a complex of the Kir6.0 subunit, a member of the inwardly rectifying K+ channel subfamily Kir6.0, and the sulfonylurea receptor (SUR) subunit, a member of ATP-binding cassette (ABC) superfamily; the functional diversity of the various KATP channels is being determined by a combination of the Kir6.0 subunit (Kir6.1 or Kir6.2) and the SUR subunit (SUR1 or SUR2) comprising it. Recent studies of the KATP channels have suggested mechanisms of KATP channel regulation and pathophysiology and also a new model in which ABC proteins regulate the functional expression of ion channels.
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  • Toshifumi TAKENAKA, Tadashi KAWAKAMI, Hideaki HORI, Yoko HASHIMOTO, Hi ...
    1998 Volume 48 Issue 6 Pages 413-420
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
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  • Masato KONISHI
    1998 Volume 48 Issue 6 Pages 421-438
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    This review summarizes estimates for cytoplasmic-free concentrations of Ca2+ ([Ca2+]i) and Mg2+ ([Mg2+]i) at rest and during contraction of skeletal muscles, from which substantial quantitative information about them has been accumulated. Although the estimates of resting [Ca2+]i in the literature widely differ, which is because of the variety of difficulties related to different methodologies used, recent studies suggest that estimates of resting [Ca2+]i of approximately 0.05-0.1 μM are likely to be correct. Following action potential propagation, the Ca2+ release from the sarcoplasmic reticulum causes a transient rise of [Ca2+]i (Ca2+ transient). The large peak amplitude and brief time course of the Ca2+ transients have been established only recently by studies with low-affinity Ca2+ indicators developed in the past decade. These technical improvements in [Ca2+]i measurements have made it possible to study relationships between [Ca2+]i and force in intact muscle fibers. in the second part of this review, various estimates of [Mg2+]i in the resting muscle are discussed. Relatively recent estimates of the [Mg2+]i level appear to be about 1.0 mM. Using the current knowledge of concentrations and reaction properties of intracellular Ca2+ -Mg2+ binding sites, we constructed a model for dynamic Mg2+ movement following Ca2+ transients. The model predicts that with a train of action potentials, the sustained rise of [Ca2+]i produces an elevation of [Mg2+]i of about 220 μM.
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Regular Papers
  • Kou UCHIDA, Michael REILLY, Donald J. ABRAHAM, Toshio ASAKURA
    1998 Volume 48 Issue 6 Pages 439-444
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    Theoretically, if the arterial partial oxygen pressure (PaO2) does not change, a right shift in the oxygen equilibrium curve (OEC) of hemoglobin should reduce arterial oxygen saturation. In this study we investigate whether a right shift in the OEC of hemoglobin decreases transcutaneous oxygen saturation (Tc-SO2) following the administration of an allosteric effector, 2-[4-(((3, 5-dichloroanilino)-carbonyl) methyl) phenoxy]-2-methylpropionic acid (RSR-4). The effect of RSR-4 on hemoglobin oxygen affinity was studied in four New Zealand white male rabbits. Following intraperitoneal administration of RSR-4, Tc-SO2 decreased in a dose-dependent manner. P50 (partial oxygen pressure at 50% hemoglobin oxygen saturation) in whole blood increased as the concentration of RSR-4 increased. Tc-SO2 decreased as whole-blood affinity (1/P50) decreased. There was no positive correlation between Tc-SO2 and PaO2. We concluded that a decrease in hemoglobin oxygen affinity following RSR-4 administration reduced arterial oxygen saturation. This decrease in the presence of an allosteric effector such as RSR-4 in vivo can be detected and monitored as a reduction in Tc-SO2.
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  • Shinyu LEE, Yoshimi OHGA, Hideo TACHIBANA, Yi SYUU, Haruo ITO, Mine HA ...
    1998 Volume 48 Issue 6 Pages 445-455
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    Recently we have shown that the left ventricular end-systolic pressure-volume relation (ESPVR) of in situ rat hearts is an upward convex curve in contrast to the linear left ventricular ESPVR in dog and human hearts. Within the smaller left ventricular volume range, the left ventricular end-systolic pressure rose steeply with increases in left ventricular volume, but it gradually reached a plateau at the larger left ventricular volumes. In adult rat hearts, the myosin isozyme is V1, unlike V3 in dog and human hearts. To investigate whether myosin isozyme affects the curvilinearity of the left ventricular ESPVR, we evaluated the left ventricular ESPVR in hypothyroid rats in which the left ventricular myosin isozyme had been shifted to V3. in the hypothyroid rats, the left ventricular contractility was depressed and the ESPVR became closer to linear. However, after dobutamine administration the ESPVR returned to curvilinear. In normal rats the curvilinearity of the left ventricular ESPVR was decreased by negative inotropic agents such as adrenergic blockers. These results indicate that the depressed left ventricular contractility in the hypothyroidism make ESPVR linear and that the enhanced left ventribular contractility from dobutamine make it curvilinear. We concluded that the curvilinearity of the rat left ventricular ESPVR is not determined by myosin isozyme per se, but by the left ventricular contractility.
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  • Kenro IMAEDA, Takashi JOH, Yoshimichi YAMAMOTO, Makoto ITOH, Hikaru SU ...
    1998 Volume 48 Issue 6 Pages 457-465
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    Inhibitory neurotransmission in guinea pig lower esophageal sphincter (LES) muscles was investigated by using electrophysiological methods. Transmural nerve stimulation (TNS) initiated an inhibitory junction potential (i.j.p.); the amplitude increased 35% by atropine (10-6 M) and converted to a muscarinic excitatory junction potential (e.j.p.) by apamin (10-7 M) plus Nω-nitro-L-arginine (L-NNA, 10-5 M). In atropinized tissue, the i.j.p. amplitude was reduced 58% by guanethidine (5×10-6 M), 41% by L-NNA (10-5 M), 57% by suramin (10-4 M), and it was abolished by apamin (10-7 M), suggesting that this potential was produced by ATP and nitric oxide (NO) released from adrenergic and nitrergic nerves, respectively, through the activation of Ca2+ -sensitive K+ channels. Hyperpolarizations produced by ATP and NO were inhibited by apamin. The i.j.p. amplitude was reduced after desensitizing the membrane with ATP. In atropinized tissue, TNS produced a relaxation that was reduced 15% by guanethidine (5×10-6 M), 50% by L-NNA (10-5 M), and 30% by apamin (10-7 M). Thus the LES receives cholinergic excitatory and adrenergic and nitrergic inhibitory innervations; the latter two components contribute evenly to the i.j.p. generation. The relaxation is mainly produced by NO in a membrane potential-independent way.
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  • Manabu KUBOKAWA, Shigeyuki NAKAYA, Yoshichika YOSHIOKA, Kazuyoshi NAKA ...
    1998 Volume 48 Issue 6 Pages 467-476
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    The inwardly rectifying K+ channel with an inward conductance of about 90 pS in the surface membrane of cultured opossum kidney proximal tubule (OKP) cell is activated by cyclic AMP-dependent protein kinase (PKA). In this study, we further exmined the involvement of the guanosine 3′, 5′-cyclic monophosphate (cGMP)-dependent process in modulation of this K+ channel by using the patch-clamp technique. In cell-attached patches, channel activity was increased by the application of either N2, 2′-O-dibutyrylguanosine 3′, 5′-cyclic monophosphate (DBcGMP, 100 μM) or 8-bromoguanosine 3′, 5′-cyclic monophosphate (8BrcGMP, 100 μM), and it was inhibited by KT5823 (10 μM), a membrane-permeable specific inhibitor of cGMP-dependent protein kinase (PKG). The effect of DBcGMP on channel activity was abolished by the pretreatment of cells with KT5823 (10 μM), but it was observed in the presence of KT5720 (200 nM), a specific inhibitor of PKA. Furthermore, atrial natriuretic peptide (ANP, 10 nM) increased channel activity, which was also prevented by the application of KT5823 (10 μM). In inside-out patches, ATP (3 mM) was required to maintain channel activity, which was inhibited by KT5823 (10 μM), but it was not increased by cGMP (100 μM) alone. The channel activity was increased by the coapplication of PKG (500 U/ml) and cGMP (100 μM). These results suggest that cGMP activates the inwardly rectifying K+ channel in OKP cells through PKG-mediated phosphorylation processes independent of PKA-mediated processes, and that ANP is an agonist which stimulates PKG-mediated processes in the proximal tubule cell. Furthermore, it is suggested that the ATP-dependent channel activity in inside-out patches is maintained at least in part by PKG, which is the membrane-bound catalytic domain.
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  • Takakazu KOBAYASHI, Makoto SHIMO, Haruo SUGI
    1998 Volume 48 Issue 6 Pages 477-482
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    Heat production in skeletal muscle has been studied with a thermopile consisting of several thermocouples in contact with muscle surface, and the experimental results have been interpreted on the assumption that heat is produced in a uniform manner. In the present study we have examined the temperature distribution of bullfrog sartorius muscle by the technique of infrared thermography, in which muscle temperatures at various regions can be measured and displayed as a thermogram on the monitor screen without thermal contact. It was found that in the muscle at rest and during an isometric tetanus, the temperature was not uniform, but differed from region to region. The amount of heat production during an isometric tetanus also differed from region to region, but the time course of heat production was nearly uniform in every region. By putting position markers on the muscle surface, it was possible to record muscle segment length changes together with temperature changes. It was found that during an isometric tetanus, the tibial region was stretched by the other regions, and the amount of heat produced was significantly greater in the other regions than in the tibial region. The application of infrared thermography in muscle energetics studies seems promising if the sensitivity of infrared detectors is improved.
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  • Sadiye ATES, Ziya KAYGISIZ
    1998 Volume 48 Issue 6 Pages 483-491
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    The involvement of nitric oxide (NO), muscarinic receptors, prostaglandins, calcium influx via slow calcium channels, Ca2+ release from intracellular stores, protein kinase C, and endothelium in the positive inotropic, negative chronotropic, and coronary vasoconstrictor effects of acetylcholine (ACh) has been investigated in isolated rat hearts. The perfusion of hearts with ACh (10-7, 5×10-7, and 10-6 M) produced marked decreases in heart rate and coronary flow and a marked increase in contractile force. Similar effects have been observed during the perfusion of hearts with ACh in the presence of Nω-nitro-L-arginine methyl ester (L-NAME), which is an inhibitor of NO synthesis. The positive inotropic, negative chronotropic, and coronary vasoconstrictor effects of ACh were abolished by muscarinic receptor blocker atropine. In hearts pretreated with cyclooxygenase inhibitor indomethacin, ACh significantly decreased heart rate but did not significantly affect coronary flow and contractile force. In the presence of calcium channel antagonist verapamil or protein kinase C inhibitor staurosporine, ACh produced a significant drop in heart rate but did not significantly affect coronary perfusion pressure and force of contraction. In the presence of the inhibitor of the release of Ca2+ from intracellular stores dantrolene sodium, ACh produced a significant increase in coronary perfusion pressure and a marked decline in heart rate, but did not significantly affect force of contraction. Furthermore, the disruption of endothelium by perfusing the hearts with saponin abolished the vasoconstrictor effect of ACh but did not alter negative chronotropic and positive inotropic effect. Our results suggest that ACh causes vasoconstrictor, negative chronotropic, and positive inotropic effects in isolated rat hearts. Cardiac effects of ACh are related to muscarinic receptor activation, and prostaglandins modulate ACh-induced vasoconstriction and positive inotropy. Our data also suggest that protein kinase C and calcium influx from extracellular source may be responsible for the vasoconstrictor and positive inotropic effect of ACh. The calcium release from intracellular stores may mediate the positive inotropic effect, and the vasoconstrictor effect of ACh depends on an intact endothelium.
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  • Ichiro SHIMOYAMA, Toshihiko ITO, Tadahiko SHIBATA, Dilshat ABLA, Yoshi ...
    1998 Volume 48 Issue 6 Pages 493-497
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    Hemispheric dominance in contextual recognition is now under discussion. Auditory event-related potentials (ERPs) with a contextual decision task were recorded to study hemispheric dominance by using the wave energy and amplitudes of N400 for eight native volunteers. Two types of 80 sentences with four clauses were used as the structure: [subject]+[object or complement]+{object]+[two-syllable verb]. One type was congruent and the other deviated at the terminal clause as an incongruent sentence. Twenty-one channel ERPs were triggered at the verbs and recorded during −200 and 1, 000 ms, with a noncephalic reference from 0.05 to 30 Hz. The wave energy was calculated as mean square potentials and was normalized with the background activity (pretrigger 200 ms). The amplitudes of N400 showed significant differences between the incongruent and congruent sentences, but the hemispheric dominance for the amplitudes of N400 was not significant between the incongruent and congruent sentences. Reaction times with the index finger to respond to the deviated verbs were 470.0 (mean)±42.5 (SD) ms. The maximum normalized wave energy within the mean reaction time showed significant differences between the incongruent and congruent sentences, and the left hemispheric energy was shown to be significantly higher than the right one.
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  • Motoyuki HASHIBA
    1998 Volume 48 Issue 6 Pages 499-504
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    Postural sway was measured in 24 healthy subjects after running or walking with eyes open on a standard treadmill exerciser. The speeds of running and walking were set at 10 and 7 km/h, respectively, and locomotion wasmaintained for 7 min. The postural sway response was characterized by systematic forward displacement followed by gradual decay to baseline and was accompanied by self-motion perception. Mean fore-back postural after sway was significantly greater after treadmill running than after normal running. The aftereffects of treadmill walking were significantly less than those of treadmill running. The 6 subjects showing distinct forward postural sway after treadmill walking were instructed to walk on the treadmill with their eyes closed. After this, none of the 6 subjects felt self-motion perception and had no evidence of postural aftersway. These results clearly demonstrate that vision during treadmill locomotion plays an important role in evoking postural sway after treadmill locomotion. It can be inferred that somatosensory/motor signals may be stored during visual-somatosensory/motor conflict and that this stored information may evoke postural change and self-motion perception.
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Short Communication
  • Kazuo HORI, Tohru ISHIGAKI, Katsuhiro KOYAMA, Mitsuharu KAYA, Junzo TS ...
    1998 Volume 48 Issue 6 Pages 505-508
    Published: 1998
    Released on J-STAGE: May 31, 2002
    JOURNAL FREE ACCESS
    Male Wistar rats, aged 6 weeks were maintained at 25°C for 9 to 11 weeks (W grop), at 10°C for 9 to 11 weeks (C group), and at 25°C for 2 weeks after exposure to 10°C for 9 weeks (D group). Thermogenesis at 10°C was significantly greater than at 25°C. Thermogenesis per body mass in the C group was greater than in the W and D groups. The RQ value at 10°C was greater than at 25°C in the W group, whereas the opposite was observed in the C and D groups. It is suggested that a large part of enhanced thermogenesis, caused by cold acclimation for 9 weeks, is lost because of a decreased secretion of calorigenic hormones, in spite of a slight decrease in BAT mass, during deacclimation for 2 weeks.
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