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Volume 48, Issue 1
Displaying 1-13 of 13 articles from this issue
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Regular Papers
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Manabu KUBOKAWA, Yoshiaki MORI, Katsuhisa FUJIMOTO, Takahiro KUBOTA1998 Volume 48 Issue 1 Pages 1-8
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSThe present study investigated basolateral K+ channels and their pH-sensitivity in isolated bullfrog proximal tubule cells by using the patch-clamp technique, and compared channel activity with the basolateral membrane potential (EM) and intracellular pH (pHi) monitored by using double-barreled H+-selective microelectrodes in perfused bullfrog proximal tubules. In the patch-clamp experiments, K+ channels with inward slope conductance of about 50 pS were observed in the basolateral membrane of isolated proximal tubule cells in cell-attached patches. Raising pH of the bath with HCO3--free HEPES Ringer solutions from 7.7 (control) to 8.2 in the presence of an H+ ionophore, FCCP (2 μM), enhanced channel activity to 126.4% of controls; lowering bath pH to 7.2 and to 6.7 reduced channel activity to 26.4 and to 1.7% of controls. Microelectrode experiments in bullfrog proximal tubules perfused with HCO3--free HEPES Ringer solutions showed that EM and pHi in control conditions of peritubular pH 7.7 without FCCP were −52.6mV and 7.45. Raising peritubular pH to 8.2 in the presence of FCCP (2μM) increased EM and pHi to −61.8mV and 7.73; lowering it to 7.2 and to 6.7 decreased EM and pHi to −28.6 mV and 7.25 and to −10.6 mV and 6.95. These results suggest that changes in EM in response to cellular alkalinization or acidification made by HCO3--free HEPES solutions are produced primarily by changes in activity of the pH-sensitive K+ channels.View full abstractDownload PDF (872K) -
Kazuki MATSUURA, Yasuaki KAWAI1998 Volume 48 Issue 1 Pages 9-15
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSThe acute changes in choroidal blood flow during postischemic reperfusion were investigated by using laser Doppler flowmetry in young (4 months) and aged (more than 18 months) Wistar rats under normothermic and hypothermic conditions. Choroidal blood flow was measured by using a laser Doppler probe attached to the scleral surface before, during, and after temporary ischemia produced by an elevation of intraocular pressure up to 80 mmHg. Body temperature was maintained either from 38 to 39°C (normothermia) or from 30 to 33°C (hypothermia). Under the normothermic condition, postischemic reperfusion showed hyperperfusion dominantly in all groups (117.1±4.9% of the baseline value after 10 min of ischemia, 208.6±16.1% after 30min, and 176.6±17.1% after 50 min). Exposure to hypothermia attenuated the postischemic hyperperfusion (101.9±11.7% after 10 min of ischemia, 152.9±11.2% after 30 min, and 107.8±19.9% after 50 min). In aged rats, the response of choroidal blood flow during reperfusion was variable. The no-reflow phenomenon was observed in 1 of 5 rats, marked hyperperfusion (238 and 177%) in 2 rats, and a small mag-nitude (127 and 115%) of hyperperfusion in the other 2 rats, whereas marked hyperperfusion was observed in all rats of the young group after 30 min of ischemia. These results suggest that hyperperfusion is dominant during the acute phase of postischemic reperfusion in young rats under normothermia. Hypothermia attenuates the postischemic hyperperfusion of the choroidal blood flow. The circulatory response during postischemic reperfusion becomes variable with age.View full abstractDownload PDF (793K) -
Miharu MIYAMURA, Koji ISHIDA, Hiroshi ITOH, Tetsuo OHKUWA1998 Volume 48 Issue 1 Pages 17-23
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSThis study was performed to test the hypothesis that potassium concentration in arterialized blood may be closely related to maximal pulmonary ventilation (VEmax) obtained at exhaustion during maximal exercise in man. Eleven healthy men performed bicycle exercise with incremental loading at 60 rpm until exhaustion. Pulmonary ventilation (VE), oxygen uptake (VO2), and heart rate (HR) were determined continuously throughout the experiment. Arterialized venous blood samples were collected to measure potassium ([K+]), lactate ([La]), hydrogen ion (pH), catecholamine ([CA]), and dopamine ([DA]) concentrations. A significant correlation (r=0.98-0.88) between VE and [K+], [La], and pH during exercise was observed in all subjects. Furthermore, a close relationship was found in this study between dopamine concentration measured at exhaustion ([DA]0) and maximal pulmonary ventilation per kilogram of body weight (VEmax/W) (r=−0.668, p<0.05) or maximum oxygen uptake per kilogram of body weight (VO2max/W) (r=0.720, p<0.05). However, no significant correlation was found between VEmax/W and [K+]0 (r=0.202, NS), [La]0 (r=−0.096, NS), and pH0 (r=0.344, NS). These results suggest that dopamine may play a more important role in the determination of maximal pulmonary ventilation during exercise in man than K+ or pH.View full abstractDownload PDF (818K) -
Akira SETOGAWA, Yasuaki KAWAI1998 Volume 48 Issue 1 Pages 25-31
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSThis study investigates changes in intraocular pressure (IOP) in rabbits during head-down tilt (HDT), which is commonly used as an experimental model to simulate microgravity. IOP was measured by the needle insertion technique (IOPNEEDLE) and Tono-pen tonometry (IOPTONO-PEN). Although the absolute value of the IOPTONO-PEN was significantly smaller than that of the IOPNEEDLE, a significant correlation (r=0.99) was observed between them. A linear regression analysis yielded an equation as follows: IOPTONO-PEN=0.67 IOPNEEDLE−0.67. Both the IOPNEEDLE and the IOPTONO-PEN changed depending on the tilt angle. Tilting from horizontal (0°) to 75° head-down increased the IOPNEEDLE and the IOPTONO-PEN by 7.3±0.8 (mean±SEM) mmHg and 4.4±1.3mmHg. The IOPNEEDLE elevated from 13.1±1.3 to 16.9±1.0mmHg immediately after the onset of 45° HDT and then gradually declined. The value of the IOPNEEDLE during 8h of HDT was significantly higher than the value in the control animals, which were kept at the horizontal prone position throughout the experiment. Similar findings were observed in the IOPTONO-PEN. These results suggest that the needle insertion technique and the Tono-pen tonometry are both useful for measuring IOP in rabbits.View full abstractDownload PDF (707K) -
C.N. WEI, Y. OHIRA, T. TANAKA, H. YONEMITSU, A. UEDA1998 Volume 48 Issue 1 Pages 33-37
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSOsteoporosis due to mineral loss is a major health problem resulting from long-term spaceflight. The development of a suitable countermeasure is essential because an advanced decrease in bone density could be irreversible. Therefore the current study was performed to test our hypothesis that the loading of bones by electrical stimulation-induced muscle contraction may prevent the mineral loss caused by gravitational unloading and bone growth will be maintained. During 10 d of hindlimb suspension, electrical stimulation at 1, 50, or 100 Hz was administered through the left sciatic nerve at the gluteal region of rats with approximately 300 g body weight. The dry weight, mineral content, and mineral density in hindlimb bones were analyzed. The dry weight and mineral content of femur and tibia-fibula in hindlimb-suspended rats tended to be less than in the age-matched cage controls. However, these detrimental effects were prevented by stimulation at 50 and 100 Hz. A positive effect of stimulation was seen even in the nonstimulated limb, although greater effect was induced in the stimulated limb. It is suggested that loading by stimulation-induced muscle contraction at higher frequencies is beneficial for the maintenance of bone growth or the prevention of mineral loss, or both, during hindlimb suspension in rats.View full abstractDownload PDF (547K) -
Tateo OGURA, Hirosuke KOBAYASHI, Michihiro SUZUKI, Tetsuya SATO, Tomoy ...1998 Volume 48 Issue 1 Pages 39-47
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSThe hypothesis of this study was that hypoxemia after methacholine (MTH) inhalation is related not only to ventilation/perfusion inhomogeneity, but also to posthyperventilation hypoxemia. To test the hypothesis, we paid special attention to changes in gas exchange and ventilation parameters after MTH inhalation. Six stable asthma patients were investigated, and SaO2, minute ventilation (VE), oxygen uptake rate in the lung (VO2), carbon dioxide output rate in the lung (VCO2), and respiratory exchange ratio (R) were measured. The SaO2 level decreased from a baseline level (before MTH inhalation) of 96.8±1.0% (mean±SD) to the lowest level (the nadir SaO2) of 89.8±2.1% (p<0.01) in 200±50s after MTH inhalation and gradually increased toward the baseline level. VCO2 increased just after MTH inhalation (post-MTH) with increased VE, and decreased at the nadir SaO2 with baseline VE and PaCO2, indicating a decrease in breath-by-breath VA and an increase in dead space minute ventilation at the nadir SaO2, but VO2 remained close to constant. R increased post-MTH, decreased at the nadir SaO2, and thereafter increased gradually toward the baseline level with a time constant of 5.6 min. The addition of CO2 to inspired air partially suppressed hypoxemia. The consensus is that hypoxemia after MTH is solely attributable to the ventilation/perfusion inhomogeneity, but posthyperventilation hypoxemia is another reasonable interpretation of the hypoxemia after MTH with decreased VA, VCO2, and R. It is speculated that posthyperventilation normoventilation in respect to VCO2 with baseline PaCO2 after MTH inhalation resulted in posthyperventilation hypoxemia as a result of relative hypoventilation in respect to VO2.View full abstractDownload PDF (987K) -
Nazrul ISLAM, Shrabani CHANDA, Tapan Kumar GHOSH, Chandan MITRA1998 Volume 48 Issue 1 Pages 49-55
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSIn an ovariectomized rat model of osteoporosis, the effects of cold stress on intestinal Ca2+ transference and rate of bone turnover were evaluated. In the ovariectomized rats, a significant reduction in intestinal transference of Ca2+ was associated with decreased activities of intestinal mucosal enzymes, alkaline phosphatase (AP), and calcium ATPase (Ca2+-AT-Pase) in all the different segments of small intestine in a descending gradient. The development of a high rate of bone turnover and osteoporosis in these animals was confirmed by significant alteration in plasma AP activity and calcium (Ca) level, urinary excretion of Ca and phosphate, and Ca: creatinine ratio. Cold stress in this model, apart from its unique influence in elevating plasma corticosterone and thyroid hormone level, enhanced all the above referred parameters studied in connection with intestinal transference of Ca2+, bone turnover rate, and osteoporosis. The results of this study emphasize that cold stress may have a positive influence on bone loss for an early development of hypogonadal osteoporosis in rats.View full abstractDownload PDF (1112K) -
Takashi KAWABATA1998 Volume 48 Issue 1 Pages 57-62
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSThermoregulatory response during exercise was studied in rats with three hydration states: euhydration, hypohydration (−18% plasma volume by thermal dehydration), and hyperhydration (+24% plasma volume by 5% bovine serum albumin solution infusion). Rats exercised (12.5 m·min-1) for 30 min at an ambient temperature of 25°C. Abdominal temperature (Tab) and heart rate were continuously recorded by using a surgically implanted transmitter and telemetry system, and the tail skin temperature (Tts) was measured as an index of peripheral vasomotor tone. In the euhydration group, Tts showed an increase when Tab reached 37.6°C; an increase of Tts was observed at 37.9°C of Tab in the hypohydration group and at 37.4°C in the hyperhydration group. The slope of the Tts-Tab relationship was steeper in the hyperhydration group and less steep in the hypohydration group than in the euhydration group. These results indicate that hypohydration leads to an upward shift in the body temperature threshold for tail vasodilation and an increase in Tab during exercise. Hyperhydration, however, leads to a downward shift of the threshold and the maintenance of a lower Tab. An elevation of the threshold Tab for vasodilation was observed when plasma volume was reduced by more than 20%, and a decrease was observed when plasma volume increased more than 15%.View full abstractDownload PDF (690K) -
M. DOI, Y. KAWAI1998 Volume 48 Issue 1 Pages 63-69
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSChanges in intracranial pressure (ICP) resulting from head-down tilt (HDT) were studied in rabbits, and a possible role of edema formation in the change of ICP was examined. Animals were anesthetized with pentobarbital sodium and artificially ventilated. ICP was continuously monitored through a catheter inserted into the subarachnoid space, It increased depending on the tilt angle and decreased when the tilt angle was reduced. ICP elevated from 4.6±0.7 mmHg (mean±standard error of the mean) at horizontal prone position to 13.7±1.0 mmHg immediately after the onset of 45° HDT and gradually reduced toward the pre-HDT baseline in the next 8h. ICP decreased below the pre-HDT baseline value immediately after returning to the horizontal prone position, and gradually increased toward the baseline during the 2h of recovery period. Histological examination (HE stain) demonstrated that exposure to 8h of HDT did not cause remarkable edema in either the gray matter or the white matter in rabbits. Water content and specific gravity of brain tissues both were increased in the HDT group in comparison with the control group. These results suggest that edema formation plays little role in the elevation of ICP during the acute phase of HDT in rabbits.View full abstractDownload PDF (1089K) -
Yoshihiko TADA, Yoshiyuki HORIO, Yoshihisa KURACHI1998 Volume 48 Issue 1 Pages 71-80
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSInwardly rectifying K+ (Kir) channels are considered to play the major role in the spatial buffering of glial cells. We have examined the electrophysiological properties of Kir channels in isolated rabbit Müller cells (retinal glial cells). Although a previous study reported that three kinds of Kir channels with different conductance and rectification properties were expressed in distinct regions of rabbit Müller cell membrane, we could record only a single population of Kir channels from the distal end to the endfoot in 205 successful cell-attached patches. The identified Müller cell Kir channel had a unitary conductance of 25 pS in the inward direction with symmetrical 153 mM K+ condition. The conductance and gating properties of the Müller cell Kir channels were identical to those of the KAB-2/Kir4.1 heterologously expressed in a mammalian cultured cell line, HEK293T cells. Thus KAB-2/Kir4.1 was the predominant glial Kir channel not only in the brain, but also in the retina. Because its rectification is intermediate, this Kir channel may contribute to both the intrusion and the extrusion of K+ ions across glial cell membrane and may be the major pathway for redistribution of extracellular K+ ions in the central nervous system.View full abstractDownload PDF (1212K) -
Kenji HIRAHARA, Taro MATSUBAYASHI, Hiroshi MATSUURA, Tsuguhisa EHARA1998 Volume 48 Issue 1 Pages 81-89
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSThe effects of various [Mg2+]i, particularly low [Mg2+]i, on the delayed rectifier K+ current (IK) were studied in guinea pig ventricular myocytes with the patch clamp technique. The magnitude of IK was evaluated from the amplitude of its tail current elicited on repolarization following the depolarizing steps. The pipette-perfusion technique was also used. The initial variations of IK magnitude were dependent on [Mg2+]i in the internal solutions with which the whole-cell recording was begun. With 0.03 to 1 mM [Mg2+]i, IK was relatively stable after patch rupture, showing a minimal decay with time; with 3 mM [Mg2+]i, IK rapidly declined; with [Mg2+]i, less than 0.01 mM IK transiently increased after patch break, but declined progressively thereafter as the magnitude of IK decreased to about 30% of the initial magnitude in 10min. The decline of IK at low [Mg2+]i showed the following features. The decline was accompanied little by changes in the voltage-activation relation or by changes in the kinetics of current deactivation. The decline was not related to changes in [Ca2+]i and was also observed in ATPγS-loaded, isoprenaline-stimulated cells, in which IK channels were presumed to be persistently phosphorylated. An application of okadaic acid did not prevent the decline of IK during Mg2+ depletion. It is suggested that a presence of [Mg2+]i higher than 0.01 mM is required to maintain IK in guinea pig ventricular cells. The depression of IK at low [Mg2+]i appears to involve a phosphorylation-dephosphorylation-independent mechanism.View full abstractDownload PDF (1057K)
Short Communications
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Michiki KASAI1998 Volume 48 Issue 1 Pages 91-93
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSA problem of the analysis of bell-shaped dose-response curves was theoretically discussed by using the response of ryanodine receptors for Ca2+ concentration as a model case. Usually the response curves were analyzed under the assumption that the receptor has a high affinity activation site and a low affinity inhibition site. However, a solution having a low affinity activation site and a high affinity inhibition site can be deduced theoretically from the same data. A method to avoid an erroneous result was proposed.View full abstractDownload PDF (308K) -
Ken AOKI, Narihiko KONDO, Manabu SHIBASAKI, Seiji TAKANO, Tetsuo KATSU ...1998 Volume 48 Issue 1 Pages 95-98
Published: 1998
Released on J-STAGE: May 31, 2002
JOURNAL FREE ACCESSSix male subjects had their lower legs immersed in water at 42°C for 60 min at 4 different times of the day to study whether the skin blood flow response to passive heat stress shows circadian variation in the relationship between skin blood flow and local sweating rate. When skin blood flow was plotted against local sweating rate, three distinct phases were observed. Phase A, an increase in skin blood flow without sweating was maximal at night. But the slope of the regression line did not change over the day in Phase C. These findings suggest that there is circadian variation in the skin blood flow response before onset of sweating during passive heat stress. This variation might be related, in part, to the circadian rhythm in vasoconstrictor activity.View full abstractDownload PDF (451K)
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