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Biomedical subjects

E Tanaka

Publications and source records attributed to E Tanaka.

At least 253 records · Page 14Linked to original sources
PubMed1997

Expression of Fas in renal cell carcinoma.

We have investigated whether the Fas-mediated cell death pathway is functional in renal cell carcinoma. The expression of Fas in surgical specimens and cell lines of renal cell carcinoma was examined. Fas expression was positive in six out of 18 tumors measured by flow cytometry and was prominent in advanced tumors. Three out of the six Fas-positive tumors had already metastasized at the time of surgery. A significant correlation was found between the tumor volume and the percentage of Fas-positive cells in a tumor (r = 0.70, P = 0.0007). Fas-positive tumors were larger than Fas-negative tumors [mean tumor volume (ml) +/- SD, Fas(+), 265.6 +/- 136.8; Fas(-), 65.8 +/- 80.9, P = 0.0012]. All human renal carcinoma cell lines tested (ACHN, Caki-1, SMKT-R-2, SMKT-R-3 and SMKT-R-4) expressed Fas abundantly, as Fas-positive cells accounted for > 50% in all cell lines by flow cytometry. Treatment with anti-Fas antibody caused apoptosis in Fas-positive renal cell carcinoma cell lines. However, the effectiveness of apoptosis induction in individual cell lines was not correlated with the level of Fas expressed. These data suggest that Fas targeting may be a therapeutic option for treatment of advanced renal cell carcinoma which is refractory to either chemotherapy or irradiation.

Apoptosis↗
PubMed1997

Antibody response to E2/NS1 hepatitis C virus protein in patients with acute hepatitis C.

Antibody response to the E2/NS1 protein of the hepatitis C virus (HCV) was studied in 26 patients with post-transfusion acute hepatitis C. Second-generation HCV (HCV-2) antibody, E2/NS1 antibody and HCV-RNA were measured in serial serum samples taken within 1 month and 3, 6 and 12 months after the onset of acute hepatitis C. The HCV genotype was also tested to study its clinical significance. Of 26 patients, eight showed normalization of alanine aminotransferase (ALT) and clearance of HCV-RNA (resolved group). In the remaining 18 patients, HCV viraemia and ALT abnormality (except one patient) continued for more than 3 years (unresolved group). Both HCV-2 and E2/NS1 antibodies were positive at least once in all patients. The prevalence of E2/NS1 antibody was significantly (P < 0.05) higher in the resolved group (88%) than in the unresolved group (39%) in the period within 1 month of onset; the prevalence was similar between the two groups thereafter. The prevalence of HCV-2 antibody did not differ between the two groups at any point. The HCV genotype was not related to the chronicity of acute hepatitis C. In conclusion, the E2/NS1 antibody appeared in all patients with acute hepatitis C and was associated with the clearance of HCV.

Acute Disease↗
PubMed1997

Clinical significance of hepatitis G virus infection in patients on long-term haemodialysis.

Infection with the newly discovered hepatitis G virus (HGV) was analysed in 163 patients on long-term haemodialysis to clarify its prevalence and clinical significance. Hepatitis G virus RNA in serum was measured by polymerase chain reaction with primers corresponding to the putative non-structural 5' region. Of the 163 patients, three (1.8%) were positive for hepatitis B surface antigen, 40 (24.5%) were positive for hepatitis C virus (HCV)-RNA and 16 (9.8%) were positive for HGV-RNA. Five of the 16 patients with HGV-RNA were also positive for HCV-RNA. Patients with HCV and HGV coinfection had undergone a longer duration of haemodialysis (P = 0.001) and had higher units of transfusion (P = 0.031) compared with those without hepatitis virus infection. Transfusion history was significantly higher (P = 0.039) in patients with only HGV infection than in those without hepatitis virus infection. Hepatitis C virus RNA concentration was higher (P = 0.032) in patients with HCV and HGV coinfection than in those with HCV infection only, but alanine aminotransferase (ALT) levels were similar between these two groups. In conclusion, about 10% of patients on haemodialysis were infected with HGV and the infection was closely associated with transfusion history.

Adolescent↗
PubMed1997

Quantitative measurement of HCV RNA in the serum: a comparison of three assays based on different principles.

Quantitative measurement of hepatitis C virus (HCV) RNA is useful in patients with chronic hepatitis C, especially with interferon treatment. We examined the clinical usefulness of the AMPLICOR monitor assay, a newly developed assay for quantitative measurement, by comparing it with two other assays with different principles. A total of 48 patients with chronic hepatitis C who were treated with interferon-alpha (IFN-alpha) were studied: 19 were complete responders and 29 were non-responders. Hepatitis C virus RNA was measured quantitatively by AMPLICOR, branched DNA (bDNA) probe, and competitive polymerase chain reaction (C-PCR) assays. An internal quantification standard was used in the AMPLICOR assay. A cDNA competitor with a deletion of 15 base pairs in the middle portion was used in the C-PCR method. The concentration of HCV RNA was significantly correlated between the three assays adopted in this study. Sensitivity of assays was 100% by C-PCR, 90% by AMPLICOR and 69% by bDNA assays. The active quantitative range was best with the C-PCR assay and worst with the bDNA assay. The bDNA assay had a tendency to exhibit lower values for patients with serotype 2 than did the other two assays. The predictive rate of the long-term response to IFN-alpha therapy, before its initiation, was over 75% in all three assays. The predictive rate just after completing IFN-alpha therapy was as high as 80% by C-PCR and the AMPLICOR assays, but was low (58%) with the bDNA assay. The handling of the bDNA and AMPLICOR assays was much easier than the C-PCR assay, which required time and skill. These results indicate that the AMPLICOR assay is a simple and reliable method for measuring the serum concentrations of HCV RNA, and thus is suitable for clinical application.

Adult↗
PubMed1997

[Clinical and diagnostic characteristics of Legionella pneumonia].

We have characterized clinical and diagnostic features in 18 cases of Legionella pneumonia. Age average of patients was 62.0 years old (male:female = 14:4) and underlying diseases were observed in 12 patients. Legionella pneumonia were diagnosed in 3, 5, 8 and 9 cases by culture, serum antibody measurement, urinary antigen detection and PCR, respectively. Sixteen cases were caused by L. pneumophila, while the other 2 cases were L. bozemanii pneumonia and L. pneumophila or L. dumoffii pneumonia. Chest X-rays of those patients showed multiple pneumonia shadows in 14 cases, alveolar shadows in 10 cases, pleural effusion in 5 cases. Blood-gas analysis on admission indicated hypoxemia in all cases with abnormal A-a DO2. Laboratory findings showed abnormal data in WBC, CRP, LDH, CPK and liver function tests (ex. GOT, GPT) in most cases. Serum antibody testing showed positive by 5 weeks after onset of pneumonia, but 10 cases of Legionella pneumonia diagnosed by other techniques were judged to be negative. In urinary antigen detection test, 6 and 2 cases showed positive 1 and 4 weeks after onset of pneumonia, respectively. Macrolide antibiotics were administered in all cases during the episode, but delay of macrolide administration was observed in 3 of 4 cases of dead outcome. Serum antibody measurement, urinary antigen detection and PCR, in addition to culture to bacteria, may be required for exact diagnosis of Legionella infection.

Adult↗
PubMed1997

Interleukin-12 gene expression in human monocyte-derived macrophages stimulated with Mycobacterium bovis BCG: cytokine regulation and effect of NK cells.

Macrophage-derived interleukin-12 (IL-12) is essential for the activation of a protective immune response against intracellular pathogens. In this study, we examined the regulation of IL-12 mRNA expression by monocyte-derived macrophages (MDM) in response to Mycobacterium bovis BCG stimulation. A reverse transcription-PCR assay detected p40 mRNA of IL-12 at 3 h and showed a peak at 6 to 12 h with a subsequent decline. Semiquantitation of mRNA levels by competitive PCR revealed that pretreatment with gamma interferon (IFN-gamma) amplified the expression approximately 100-fold, while pretreatment with tumor necrosis factor alpha (TNF-alpha) or granulocyte-macrophage colony-stimulating factor augmented this expression about 10-fold. In contrast, pretreatment with IL-10 and IL-4 inhibited IL-12 mRNA expression. These results were further confirmed by measuring the p70 bioactive protein level in each conditioned medium by an enzyme-linked immunosorbent assay. Since IL-12 mRNA expression was weak without cytokine pretreatment and IFN-gamma strongly augmented production, we speculated that IFN-gamma might have a role in BCG stimulation of IL-12 mRNA expression. Unexpectedly, the addition of three different kinds of anti-IFN-gamma antibodies and anti-IFN-gamma receptor antibody and the coaddition of anti-TNF-alpha antibody with anti-IFN-gamma receptor antibody all failed to inhibit IL-12 mRNA expression. However, the MiniMACS method used to remove NK cells from a mononuclear cell suspension inhibited the expression of p40 mRNA but not the expression of mRNA of TNF-alpha or IL-1beta. We concluded that the coexistence of NK cells was essential for the induction of IL-12 in MDM stimulated with BCG rather than through the secretion of IFN-gamma.

Cytokines↗
PubMed1997

Contribution of ATP-sensitive potassium channels to hypoxic hyperpolarization in rat hippocampal CA1 neurons in vitro.

To investigate the mechanism of generation of the hypoxia-induced hyperpolarization (hypoxic hyperpolarization) in hippocampal CA1 neurons in rat tissue slices, recordings were made in current-clamp mode and single-electrode voltage-clamp mode. Superfusion with hypoxic medium produced a hyperpolarization and corresponding outward current, which were associated with an increase in membrane conductance. Reoxygenation produced a further hyperpolarization, with corresponding outward current, followed by a recovery to the preexposure level. The amplitude of the posthypoxic hyperpolarization was always greater than that of the hypoxic hyperpolarization. In single-electrode voltage-clamp mode, it was difficult to record reproducible outward currents in response to repeated hypoxic exposure with the use of electrodes with a high tip resistance. The current-clamp technique was therefore chosen to study the pharmacological characteristics of the hypoxic hyperpolarization. In 60-80% of hippocampal CA1 neurons, glibenclamide or tolbutamide (3-100 microM) reduced the amplitude of the hypoxic hyperpolarization in a concentration-dependent manner by up to approximately 70%. The glibenclamide or tolbutamide concentrations producing half-maximal inhibition of the hypoxic hyperpolarization were 6 and 12 microM, respectively. The chord conductance of the membrane potential between -80 and -90 mV in the absence of glibenclamide (30 microM) or tolbutamide (100 microM) was 2-3 times greater than that in the presence of glibenclamide or tolbutamide. In contrast, the reversal potential of the hypoxic hyperpolarization was approximately -83 mV in both the absence and presence of tolbutamide or glibenclamide. In approximately 40% of CA1 neurons, diazoxide (100 microM) or nicorandil (1 mM) mimicked the hypoxic hyperpolarization and pretreatment of these drugs occluded the hypoxic hyperpolarization. When ATP was injected into the impaled neuron, hypoxic exposure could not produce a hyperpolarization. The intracellular injection of the nonhydrolyzable ATP analogue 5'-adenylylimidodiphosphate lithium salt reduced the amplitude of the hypoxic hyperpolarization. Furthermore, application of dinitrophenol (10 microM) mimicked the hypoxic hyperpolarization, and the dinitrophenol-induced hyperpolarization was inhibited by either pretreatment of tolbutamide or intracellular injection of ATP, indicating that the hypoxic hyperpolarization is highly dependent on intracellular ATP. It is therefore concluded that in the majority of hippocampal CA1 neurons, exposure to hypoxic conditions resulting in a reduction in the intracellular level of ATP leads to activation of ATP-sensitive potassium channels with concomitant hyperpolarization.

Adenosine Triphosphate↗
PubMed1997

Mediation by intracellular calcium-dependent signals of hypoxic hyperpolarization in rat hippocampal CA1 neurons in vitro.

In response to oxygen deprivation, CA1 pyramidal neurons show a hyperpolarization (hypoxic hyperpolarization), which is associated with a reduction in neuronal input resistance. The role of extra- and intracellular Ca2+ ions in hypoxic hyperpolarization was investigated. The hypoxic hyperpolarization was significantly depressed by tolbutamide (100 microM); moreover, the response was reversed in its polarity in medium containing tolbutamide (100 microM), low Ca2+ (0.25 mM), and Co2+ (2 mM), suggesting that the hypoxic hyperpolarization is mediated by activation of both ATP-sensitive K+ (KATP) channels and Ca(2+)-dependent K+ channels. The hypoxic depolarization in medium containing tolbutamide, low Ca2+, and Co2+ is probably due to inhibition of the electrogenic Na(+)-K+ pump and concomitant accumulation of interstitial K+. Hypoxic hyperpolarizations were depressed in either low Ca2+ (0.25 or 1.25 mM) or high Ca2+ (5 or 7.5 mM) medium (control: 2.5 mM), indicating that there is an optimal extracellular Ca2+ concentration required to produce the hypoxic hyperpolarization. Bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA)-AM (50-100 microM), procaine (300 microM), or ryanodine (10 microM) significantly depressed the hypoxic hyperpolarization, suggesting that Ca2+ released from intracellular Ca+ stores may have an important role in the generation of hypoxic hyperpolarization. The high-affinity calmodulin inhibitor N-(6-amino-hexyl)-5-chloro-1-naphthalenesulfonomide hydrochloride (W-7) (5 microM) completely blocked, whereas the low-affinity calmodulin inhibitor N-(6-aminohexyl)-1-naphthalenesulfonomide hydrochloride (W-5) (50 microM) did not affect, the hypoxic hyperpolarization. The calmodulin inhibitor trifluoperazine (50 microM) also suppressed the hypoxic hyperpolarization. In addition, calcium/ calmodulin kinase II inhibitor 1-[N,O-bis (1,5-isoquinol-inesulfonyl)-N-methyl-L-tyrosyl]-4-phenyl-pip erazine (KN-62) (10 microM) markedly depressed the amplitude and net outward current of the hypoxic hyperpolarization without affecting the reversal potential. In contrast, neither the myosin light chain kinase inhibitor 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexa-hydro-1,4-diazepin hydrochloride (ML-7) (10 microM) nor the protein kinase A inhibitor N-[2-(p-bromocinnamyl-amino) ethyl]-5-isoquinolinesulfonamide (H-89) (1 microM) significantly altered the hypoxic hyperpolarization. These results suggest that calmodulin kinase II, which is activated by calmodulin, may contribute to the generation of the hypoxic hyperpolarization. In conclusion, the present study indicates that, in the majority of hippocampal CA1 neurons, the hypoxic hyperpolarization is due to activation of both KATP channels and Ca(2+)-dependent K+ channels.

Animals↗
PubMed1997

Mechanisms underlying the rapid depolarization produced by deprivation of oxygen and glucose in rat hippocampal CA1 neurons in vitro.

Intracellular recordings were made to investigate the mechanism, site, and ionic basis of generation of the rapid depolarization induced by superfusion with ischemia-simulating medium in hippocampal CA1 pyramidal neurons of rat tissue slices. Superfusion with ischemia-simulating medium produced a rapid depolarization after approximately 6 min of exposure. When oxygen and glucose were reintroduced, the membrane potential did not repolarize but depolarized further, reaching 0 mV approximately 5 min after reintroduction. Simultaneous recordings of changes in cytoplasmic Ca2+ concentration ([Ca2+]i) and membrane potential recorded from 1-[6-amino-2-(5-carboxy-2-oxazolyl)-5-benzofuranyloxy]-2-(2- amino-5-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid pentaacetoxymethyl ester (Fura-2/AM) loaded slices revealed a rapid increase in [Ca2+]i in all CA1 layers corresponding to the rapid depolarization of the soma membrane. The result suggests that the rapid depolarization is generated not only in the soma but also in the apical and basal dendrites. Application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), DL-2-amino-4-phosphonobutyric acid, and DL-2-amino-3-phosphonopropionic acid or bicuculline did not affect the amplitude and the maximal slope. Reduction in the concentration of extracellular Ca2+ or addition of CNQX or DL-2-amino-5-phosphonopentanoic acid delayed the onset of the rapid depolarization. The amplitude of the rapid depolarization recorded with Cs acetate electrodes in tetraethylammonium-containing medium had a linear relationship to the membrane potential between -50 and 20 mV. The reversal potential was shifted in the hyperpolarizing direction by a decrease in either [Na+]o or [Ca2+]o, whereas the reversal potential was shifted in the depolarizing direction by a decrease in [Cl-]o or using CsCl electrodes. An increase or decrease in [K+]o did not affect the reversal potential. These results indicate that the rapid depolarization is Na+, Ca2+, and Cl- dependent. The lack of effects of changes in [K+]o is probably due to the accumulation of interstitial K+ before generating the rapid depolarization. Prolonged application of ouabain (30 microM) caused an initial small hyperpolarization, a subsequent slow depolarization, and a rapid depolarization. In summary, the present study has demonstrated that the rapid depolarization is voltage-independent and is probably due to a nonselective increase in permeability to all participating ions, which may occur only in pathological conditions. The underlying conductance change is primarily the result of inhibition of Na,K-ATPase activity in the recorded neuron.

Animals↗
PubMed1997

Factors that reverse the persistent depolarization produced by deprivation of oxygen and glucose in rat hippocampal CA1 neurons in vitro.

In CA1 pyramidal neurons in rat hippocampal tissue slices, superfusion with ischemia-simulating medium produced a rapid depolarization after 6 min of exposure. The membrane potential eventually reached 0 after 5 min (a persistent depolarization), even when oxygen and glucose were reintroduced. The role of various ions in the reversal of this persistent depolarization after reintroduction of oxygen and glucose was investigated. The peak of the persistent depolarization was decreased in solutions containing reduced Na+ or Ca2+ and in solutions containing Co2+ or Ni2+. In contrast, the depolarization was not affected by reduction of external K+ or Cl- or by addition of tetrodotoxin (TTX), flunarizine, or nifedipine. These results suggest that sustained Na+ and Ca2+ influxes produce the persistent depolarization. The membrane potential recovered after reintroduction of oxygen and glucose in low Ca2+, low Cl-, or K+-rich medium and in TTX- or tetraethylammonium-containing medium, but not in low Na+ or low K+ medium and in flunarizine- or nifedipine-containing medium. Either reduction in extracellular Ca2+ or addition of Co2+ was the most effective in promoting recovery from the persistent depolarization, suggesting that Ca2+ influx has a key role in causing the membrane dysfunction. The peak of the persistent depolarization was reduced by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), DL-2-amino-5-phosphonopentanoic acid (AP5), DL-amino-3-phosphonopropionic acid (AP3), or DL-amino-4-phosphonobutyric acid, suggesting that activation of non-N-methyl-D-aspartate (non-NMDA), NMDA, and metabotropic glutamate (Glu) receptors is involved in the generation and maintenance of the persistent depolarization. Among these Glu receptor antagonists, only CNQX or AP5 was able to reduce dose dependently the level of depolarization, suggesting that Ca2+ influx via both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate type II receptors and NMDA receptors contributes to the membrane dysfunction. trans-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD) did not affect the peak potential of the persistent depolarization, but it dose-dependently restored the membrane potential. AP3 antagonized the protective action of t-ACPD. The membrane potential also recovered after reintroduction when the slice was pretreated by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester, ryanodol 3-(1H-pyrrole-2-carboxylate), 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride, and procaine, suggesting that raised [Ca2+]i from Ca2+-induced Ca2+ release pool contributes to the membrane dysfunction. It, therefore, is concluded that raised [Ca2+]i has a dominant role in causing irreversible changes. The increase in [Ca2+]i during the persistent depolarization may be the result of Ca2+ entry via both a leaky membrane and Glu-activated receptor channels as well as Ca2+ released from internal stores.

Animals↗
PubMed1997

Yield of computed tomography and bronchoscopy for the diagnosis of Mycobacterium avium complex pulmonary disease.

Mycobacterium avium complex (MAC) pulmonary disease with nodules and bronchiectasis is increasing. But the usefulness of computed tomography (CT) and bronchoscopy for diagnosis and the significance of MAC isolation from respiratory secretions are still unclear. For a 4-yr period, we prospectively examined the role of bronchoscopy with bronchial washing and transbronchial lung biopsy in 26 patients who had clusters of small nodules in the periphery of the lung associated with ectatic changes of the draining bronchi on the CT scan. None of them was infected with human immunodeficiency virus. Thirteen of the 26 patients (50%) had cultures positive for MAC, six in the sputum and 13 in the bronchial washing. Epithelioid granuloma was demonstrated in eight of 13 patients with culture-positive MAC and in two of 13 patients in whom MAC was culture-negative. Rapidly growing mycobacteria were cultured in the two patients. Seven of the eight biopsy-positive patients received treatment and responded by sputum conversion and/or radiographic improvement. We found that the CT finding was a useful clue to suspect MAC pulmonary disease and that the bronchial washing was more sensitive than the routine expectorated sputum for MAC isolation. Demonstration of granuloma in more than half of the MAC-positive patients would suggest that MAC may have invaded the lung tissue rather than colonized in the airways.

Adult↗
PubMed1997

Effect of thoracic irradiation on hepatocyte growth factor in rats lung and in bronchoalveolar lavage fluid of patients with thoracic malignancies.

This study aimed to examine the physiological role of hepatocyte growth factor (HGF) after thoracic irradiation. We analysed the changes of HGF protein levels in rat lung following 12 Gy of whole thoracic irradiation. Bronchoalveolar lavage fluid (BALF) was then collected from 11 patients (10 lung cancer and one oesophageal cancer) after completion of radiation therapy. One month after irradiation, the HGF protein level in the lungs of irradiated rats decreased (p<0.05), followed by a remarkable elevation in HGF protein levels 2 (p<0.05) and 3 months (nonsignificant) after irradiation accompanied by the clinical appearance of radiation pneumonitis. Finally, HGF protein levels in the lung returned to their original level 6 months after thoracic irradiation. In humans, HGF protein levels in the BALF in the limited irradiated area were lower than those obtained from unirradiated areas (p<0.05). In conclusion, hepatocyte growth factor production is transiently suppressed in the irradiated area after irradiation.

Aged↗
PubMed1997

Tacrine improves working memory deficit caused by permanent occlusion of bilateral common carotid arteries in rats.

Effect of tacrine, a cholinesterase inhibitor, on spatial acquisition deficit caused by permanent occlusion of bilateral common carotid arteries (2VO) was examined by using the conventional 8-arm and the 4-arm baited radial maze tasks in rats. Daily administration of tacrine (0.1 and 0.3 mg/kg, i.p.) 1 month after 2VO operation significantly improved the impaired spatial acquisition in the conventional maze task. This treatment also ameliorated the 2VO-induced working but not reference memory deficit in the 4-arm baited radial maze task. These results suggest that tacrine improvement of working memory deficit in the 2VO rats is due to stimulation of central cholinergic systems.

Animals↗
PubMed1997

Renal cortical retention on delayed CT after angiography and contrast associated nephropathy.

The aim of this study was to examine the relationship between renal cortical retention (RCR) of contrast media observed on delayed CT (median delay: 20 h) and contrast associated nephropathy (CAN). We investigated the incidence of both phenomena in 270 patients. CAN was defined as an increase in the creatinine level > 0.5 mg dl-1 (44 mumol l-1) and > 25% on day 1, 3 or 7, while RCR was recognized when CT values for the renal cortex showed either mild RCR (CT value > 50) or severe RCR (CT value > 100). RCR was demonstrated in 127 patients (47%), mild in 78 (29%) and severe in 49 (18%), on delayed CT after angiography. CAN was found in eight patients (3%). Patients with severe RCR showed a higher CAN rate (8%) than other patients (mild RCR: 4%, RCR (-): 1%) (p = 0.02). The type of contrast medium was independently associated with the incidence of RCR (p = 0.0001). Although severe RCR was associated with a higher frequency of CAN than the milder forms of RCR, RCR as such was not always associated with CAN.

Adolescent↗
PubMed1997

Heat production by brown adipocytes of FOK rats genetically resistant to a hot environment.

The FOK rat was established as an inbred strain with genotypic adaptation to a hot environment. To investigate the mechanism of the heat resistance of FOK rats, heat production by isolated brown adipocytes in FOK and WKAH rats was measured at 37.0 and 39.9 degrees C. Basal heat production by brown adipocytes of FOK rats was not significantly different from that of WKAH rats. Isoproterenol increased the heat production in a dose-dependent manner in both strains, while 10(-9) M isoproterenol caused a significant increase in WKAH rats and a negligible change in FOK rats. These results indicate that the reason why FOK rats are resistant to the severe heat is partly due to the low heat production by brown adipocytes.

Adaptation, Physiological↗
PubMed1997

Contribution of mitochondria to the removal of intracellular Ca2+ induced by caffeine and rapid cooling at low temperatures in ferret ventricular muscles.

We investigated the role of mitochondria in the removal of intracellular Ca2+ which was increased by caffeine (15 mM, Caf), rapid lowering of the solution temperature from 30 to 4 degrees C (rapid cooling, RC), and electrical stimulation (0.07 Hz, ES). For this purpose, the intracellular Ca2+ concentration ([Ca2+]i) was measured using aequorin from the superficial cells of ferret papillary muscles. The three maneuvers induced transient changes in [Ca2+]i with different time courses. The decay time of the aequorin light signal (DT) in the Caf-induced Ca2+ release was significantly prolonged by the inhibitors for Na+-Ca2+ exchanger (Ni2+, Na+-free solution) at higher temperatures (> or = 12 degrees C). In the caffeine application at lower temperatures (< or = 12 degrees C), the inhibitors for mitochondria (ruthenium red, NaN3) significantly prolonged the DT but other inhibitors were ineffective. In the RC-induced Ca2+ release, DT was significantly prolonged by the mitochondrial inhibitors but other inhibitors were not effective. In the ES-induced Ca2+ release, each inhibitor for the sarcoplasmic reticulum (SR) (thapsigargin and 2,5-di(tert-butyl)-1,4-benzohydroquinone) prolonged the DT at all temperatures. The inhibitors for Na+-Ca2+ exchanger slightly prolonged the DT only at higher temperatures, and the mitochondrial inhibitors did not alter the DT at any temperature. These results suggest that mitochondria substantially transport Ca2+ when the Ca2+ uptake by the SR and Na+-Ca2+ exchanger are inhibited and [Ca2+]i is increased with a slower time course.

Aequorin↗
PubMed1997

Ca2+ release induced by rapid cooling and caffeine in ferret ventricular muscles.

The Ca2+ release induced by rapid cooling (RC) and caffeine in ferret ventricular muscles was investigated. For this purpose, the author measured the intracellular Ca2+ concentration ([Ca2+]i) using aequorin. Rapid lowering of the temperature of the bathing solution from 30 degrees C to low temperatures after the cessation of electrical stimulation transiently increased [Ca2+]i. The peak of [Ca2+]i was altered depending upon the temperature in RC. [Ca2+]i reached 1.59 microM when the temperature was lowered from 30 to 4 degrees C. Caffeine (15 mM) applied during cooling after the decline of RC-induced intracellular Ca2+ signal caused an increase in [Ca2+]i. The author assumed that the total Ca2+ content in the SR was the sum of the peaks of [Ca2+]i increased by RC (Ca(RC)) and caffeine application (Ca(caf)). The fractional Ca2+ release induced by RC [Ca(RC)/"assumed" total released Ca2+ from the SR(%)] was 63.7% at 4 degrees C. The peak of Ca2+ increased by RC was proportional to the "assumed" total released Ca2+ from the SR. No significant correlation was observed between RC-induced [Ca2+]i change and the [Ca2+]i before RC. However, in Na+-deficient solutions (Li+ or TMA+ replacement), the fractional Ca2+ release induced by RC was decreased; this inhibition shows a dependence upon extracellular Na+ concentration. In contrast, the fractional Ca2+ release by caffeine application after RC was enhanced. These results suggest that: 1) RC releases a fraction of the Ca2+ accumulated in the SR and 2) the mechanism of RC-induced Ca2+ release in mammalian cardiac muscle is different from that of RC-induced Ca2+ release in frog skeletal muscles, which requires an increase in [Ca2+]i before RC. Extracellular Na+ might modify RC-induced Ca2+ release through a change in [Na+]i.

Animals↗