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Biomedical subjects

R Sato

Publications and source records attributed to R Sato.

At least 199 records · Page 11Linked to original sources
PubMed1995

Characterization of the acetylcholine-sensitive muscarinic K+ channel in isolated feline atrial and ventricular myocytes.

M2-cholinergic receptor activation by acetylcholine (ACh) is known to cause a negative inotropic and chronotropic action in atrial tissues. This effect is still controversial in ventricular tissues. The ACh-sensitive muscarinic K+ channel (IK(ACh)) activity was characterized in isolated feline atrial and ventricular myocytes using the patch-clamp technique. Bath application of ACh (1 microM) caused shortening of action potential duration without prior stimulation with catecholamines in atrial and ventricular myocytes. Resting membrane potential was slightly hyperpolarized in both tissues. These effects of ACh were greater in atrium than in ventricle. ACh increased whole-cell membrane current in atrial and ventricular myocytes. The current-voltage (I-V) relationship of the ACh-induced current in ventricle exhibited inward-rectification whose slope conductance was smaller than that in atrium. In single channel recording from cell-attached patches, IK(ACh) activity was observed when ACh was induced in the pipette solution in both tissues. The channel exhibited a slope conductance of 47 +/- 1 pS (mean +/- SD, n = 14) in atrium and 47 +/- 2 pS (n = 10) in ventricle (not different statistically; NS). The open times were distributed according to a single exponential function with mean open lifetime of 2.0 +/- 0.3 msec (n = 14) in atrium and 1.9 +/- 0.3 msec (n = 10) in ventricle (NS); these conductance and kinetic properties were similar between the two tissues. However, the relationship between the concentration of ACh and single channel activity showed a higher sensitivity to ACh in atrium (IC50 = 0.03 microM) than in ventricle (IC50 = 0.15 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1995

Nucleotide sequence of the gene encoding novel delta-endotoxin from Bacillus thuringiensis serovar japonensis strain Buibui specific to scarabaeid beetles.

A new isolate of Bacillus thuringiensis serovar japonensis strain Buibui, which was specific to scarab beetles (M. Ohba et al., Lett. Appl. Microbiol. 14:54, 1992), was shown to have a 130-kDa insecticidal crystal protein (ICP) (H. Hori et al., J. Appl. Bacteriol. 76:307, 1994). ClaI restriction enzyme fragments of total cell DNA of the isolate were cloned into E. coli (Sato et al., Curr. Microbiol. 28:15, 1994). Whole 3480-bp nucleotide sequence of the gene encoding 130-kDa ICP was determined, and the molecular weight of the ICP was estimated to be 130,424. The strongly conserved five blocks that occur in almost all ICP genes of B. thuringiensis were detected in the ORF with the same order and almost the same intervals as elsewhere. The amino acid sequence homologies of the whole ICP or N-terminus half portion to that of the CryIIIA, B, C, D, and CryV were about 35%.

Amino Acid Sequence↗
PubMed1995

The effect of AL0671, a novel potassium channel opener, on potassium current in rat aortic smooth muscle cells.

1. We evaluated the mechanism of activation by AL0671, a novel potassium channel opener, of potassium current in rat aortic smooth muscle cells. 2. Under conditions of whole cell recording, AL0671 (1-1000 microM) markedly increased potassium current with a Hill coefficient of 2 and dissociation constant of 1.5 x 10(-4) M. This activation was completely inhibited by intracellular ATP. 3. Under inside-out patch conditions, the ATP-sensitive K+ channels (KATP) treated with AL0671 (100 microM) showed prolongation of the slower open time component and shortening of the slower closed time component without modification of channel conductance.

Animals↗
PubMed1995

Mechanism of inhibition of the sodium current by bepridil in guinea-pig isolated ventricular cells.

1. Effects of bepridil, a sodium-, calcium-, and potassium-antagonistic agent, on the Na+ current were studied by the whole cell voltage clamp technique (tip resistance = 0.5 MOhm, [Na]i and [Na]o 10 mmol l-1 at 20 degrees C). 2. Bepridil produced tonic block (Kdrest = 295.44 mumol l-1, Kdi = 1.41 mumol l-1; n = 4). 3. Bepridil (100 mumol l-1) shifted the inactivation curve in the hyperpolarization direction by 13.4 +/- 2.7 mV (n = 4) without change in the slope factor. 4. In the presence of 50 mumol l-1 bepridil, bepridil showed use-dependent block at 2 Hz, whereas changes in pulse duration did not significantly effect this use-dependent block (81% +/- 2% at 10 ms, 84% +/- 3% at 30 ms, 86% +/- 3% at 100 ms; n = 4). 5. After removal of fast inactivation of the Na+ current by 3 mmol l-1 tosylchloramide sodium, bepridil (50 mumol l-1) still showed use-dependent block which was independent of the holding potential. 6. The recovery time constant from the bepridil-induced use-dependent block was 0.48 s at holding potential of -100 mV and 0.51 s at holding potential of -140 mV. 7. These results indicate that bepridil could bind to the receptor in the sodium channel through the hydrophobic and the hydrophilic pathway and leave the receptor through the hydrophobic pathway in the lipid bilayer. The binding and dissociation kinetics of this drug were shown to be fast, and the accumulation of the drug in the sodium channel appeared to be small. Bepridil is presumed to be safe in terms of adverse effects that result from drug-accumulation in the sodium channel.

Animals↗
PubMed1995

beta-Adrenergic modulation of the inwardly rectifying potassium channel in isolated human ventricular myocytes. Alteration in channel response to beta-adrenergic stimulation in failing human hearts.

The beta-adrenergic modulation of the inwardly-rectifying K+ channel (IK1) was examined in isolated human ventricular myocytes using patch-clamp techniques. Isoproterenol (ISO) reversibly depolarized the resting membrane potential and prolonged the action potential duration. Under the whole-cell C1- -free condition, ISO applied via the bath solution reversibly inhibited macroscopic IdK1. The reversal potential of the ISO-sensitive current was shifted by approximately 60 mV per 10-fold change in the external K+ concentration and was sensitive to Ba2+. The ISO-induced inhibition of IK1 was mimicked by forskolin and dibutyrl cAMP, and was prevented by including a cAMP-dependent protein kinase (PKA) inhibitor (PKI) in the pipette solution. In single-channel recordings from cell-attached patches, bath applied ISO could suppress IK1 channels by decreasing open state probability. Bath application of the purified catalytic sub-unit of PKA to inside-out patches also inhibited IK1 and the inhibition could be antagonized by alkaline phosphatase. When beta-adrenergic modulation of IK1 was compared between ventricular myocytes isolated from the failing and the nonfailing heart, channel response to ISO and PKA was significantly reduced in myocytes from the failing heart. Although ISO inhibited IK1 in a concentration-dependent fashion in both groups, a half-maximal concentration was greater in failing (0.12 microM) than in nonfailing hearts (0.023 microM). These results suggest that IK1 in human ventricular myocytes can be inhibited by a PKA-mediated phosphorylation and the modulation is significantly reduced in ventricular myocytes from the failing heart compared to the nonfailing heart.

Adrenergic beta-Agonists↗
PubMed1995

Regulation of intracellular cholesterol metabolism.

Animal cells synthesize cholesterol from acetyl CoA through a series of more than 20 enzymatic reactions. In addition, cells obtain cholesterol from plasma in the form of low-density lipoprotein (LDL), which is internalized via the LDL receptor and hydrolyzed to free cholesterol in lysosomes. Each cell must balance these internal and external sources while avoiding sterol shortage or overaccumulation. Both the biosynthetic and uptake pathways are well-regulated through feedback control. When cells are cultured in the presence of LDL, the activity of both 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) synthase and HMG CoA reductase decline by more than 90% and the number of LDL receptors also decreases (1). In the absence of LDL, the cells maintain high activities of these two enzymes, which are rate-limiting enzymes of the biosynthetic pathway, and also maintain a large number of LDL receptors on their surface. In this review we assess recent progress in understanding the mechanisms involved in transcriptional and posttranscriptional regulation of intracellular cholesterol metabolism.

Animals↗
PubMed1995

[Characteristics of enzyme substrate used for enzyme immunoassay].

Enzyme immunoassay in measured its enzyme activity as a signal. This signal detection method have been progressing from colorimetric to fluorometric determination, and most recently amongst for more sensitive substrate chemiluminescent determination is popular. The methods, colorimetric determination is recognized to be less sensitive. We confirmed that the alkaline phosphatase labeled enzyme, cycling method significantly increased its sensitivity by changing the substrate. If the minimum detection limit is not sensitive enough by colorimetric determination, fluorometric is useful, and chemiluminescence can be applied when ultra sensitive method is required. We briefly described the characteristics of the main substrates which may very the sensitivity in these assays.

Chromogenic Compounds↗
PubMed1995

[A case report of the atypical tuberculosis associated with AIDS].

A 49-year-old Japanese male who had been imprisoned for five years then lived with other men complained of fever, constitutional symptoms and a 12 kg weight loss over four-month period. He was referred to us as his gastric washings were positive for acid-fast bacilli (AFB). Chest X-ray showed patchy, infiltrative small shadows primarily in the right upper lung field without hilar adenopathy. Before transfer to our hospital, tuberculosis chemotherapy composed of SM, INH, RFP and PZA was initiated. Over the next three weeks, fever dropped, and the above described abnormal shadows on the chest X-ray improved, leaving small cystic lesions. Although a sputum smear was negative for AFB, M. tuberculosis was isolated from cultured samples and sensitive to all standard anti-tuberculous drugs. AFB were also demonstrated on a touch imprint of biopsied cervical lymph nodes. Sputum samples turned negative one month later both on smear and culture. Moreover, high fever developed and another abnormal shadow indicative of Pneumocystis carinii (PCP) appeared in the left lung field one month after the admission. White plaque was noted in the oral cavity. Dark red nodules were observed on the upper extremities and chest wall, and diagnosed histologically as Kaposi's sarcoma. Serologic testing for HIV was positive both by PA and Western blot methods, thus AIDS was diagnosed according to the CDC surveillance case definition for AIDS with the diagnosis of tuberculosis. The patient died of wasting syndrome on the 90th hospital day. On autopsy, small thin-walled cavities were observed in the right upper lung, correlating with earlier X-ray and CT findings.(ABSTRACT TRUNCATED AT 250 WORDS)

AIDS-Related Opportunistic Infections↗
PubMed1995

A new class III antiarrhythmic drug, MS-551, blocks the inward rectifier potassium channel in isolated guinea pig ventricular myocytes.

We have studied the effects of MS-551 on the inward rectifier potassium channel (IK1) in isolated guinea-pig ventricular myocytes by use of whole-cell and single-channel recording techniques. MS-551 (5 microM) blocked the IK1 current. The percent blockade of the peak and steady-state IK1 current by MS-551 was constant at each test potential. In contrast 50 microM MS-551 failed to block either the sodium or the calcium current. Under cell-attached patch conditions, MS-551 reduced the open probability of IK1 channel activity by prolonging the interburst interval without changing either the unitary amplitude or the equilibrium potential. The blockade of IK1 was concentration-dependent. MS-551 did not change either the mean open time or mean closed time within a burst. Extracellular acidification (pH 6.4) strongly attenuated the effect of MS-551 on the open probability of IK1 channel activity when compared with its effect at pH 7.4. In summary, our results demonstrated that MS-551 blocked the IK1 channel. The neutral form of this drug molecules may penetrate the cardiac cell membrane via a hydrophobic pathway to block the steady-state IK1 current by reduction of open probability.

Animals↗
PubMed1995

Antiarrhythmic drugs inhibit the G-protein and K+ channels in the cultured thyroid cell line.

We examined the effects of antiarrhythmic drugs on the induction of cAMP by TSH (thyroid-stimulating hormone), using continuously cultured FRTL-5 rat thyroid cells. Group Ia antiarrhythmic drugs had no effect, but Group Ib antiarrhythmic drugs suppressed cAMP induction by TSH. These drugs suppressed cAMP induction in response to cholera toxin but did not inhibit TSH receptor binding or cAMP induction by forskolin. These results indicate that Group Ib antiarrhythmic drugs inhibit thyroid G-protein, resulting in a decrease in cAMP induction by TSH. We also examined the effect of antiarrhythmic drugs on K+ channels. Group Ia antiarrhythmic drugs had no effect on K+ channel activation by TSH and cAMP. On the other hand, Group Ib antiarrhythmic drugs suppressed K+ channel activation by TSH and cAMP. This indicates that the mechanism of suppression is not inhibition of TSH receptors or G-proteins but the direct suppression of K+ channels. Group Ib antiarrhythmic drugs inhibited thyroid Gs-protein and thyroid K+ channels. Considering the close relationship between G-protein and ion channels in the cardiac cell membrane, these different effects of Group Ia and Group Ib antiarrhythmic drugs on G-proteins and K+ channels are of interest. Further investigation is necessary to clarify the relationship between thyroid G-proteins and thyroid K+ channels.

Animals↗
PubMed1995

[A study on health and caregiving status of the elderly over age 75 living in urban Tokyo--comparing 1987 with 1993].

The purpose of this study is to propose the improvement of the community care service and caregivers' support system. A questionnaire was sent to the elderly over age 75 living in Chuo Ward of Tokyo, on their living place, previous illness, health status, degree of assistance needed, and their caregivers. The same kind of surveys were made in 1987 and 1993, and the health status and home care were compared and changes in caregiver services were examined. Valid responses of 3,294 (response rate of 81.3%) in 1987 and 3,409 (response rate of 76.3%) in 1993 were analyzed and compared with each other. The results are following; (1) The total number of bedridden elderly persons decreased from 214 (6.5% of the total) in 1986 to 61 (1.8% of the total) in 1993. The number of elderly over age 75 with high health status increased. (2) The rate of the elderly who stay only indoors, although physically non-handicapped and in good health, was 20%. (3) The statistic of caregivers' concern about care services in the answer to open ended questions showed the increase of the desire for the supply of information, and the fact of more suitable pieces of advice having been given about the resources for care, care-give service, and family adjustment. It is necessary to establish the system to support and develop home care in the community in the future. Social support will also be necessary not only for infirm or handicapped elderly people, but also for demented, living in solitude, or non-social withdrawn healthy aged people to make use of community care service, counseling of care service and short stay at nursing homes. Especially the importance of community care service to prevent the elderly from being bedridden was suggested. Moreover, general broad support is necessary, such as social education, income guarantee and housing measure as well as that from the point of view of health and welfare.

Activities of Daily Living↗
PubMed1995

[A study on health and caregiving status of the elderly over age 75 living in urban Tokyo--social services and caregiving for the bedridden and senile elderly].

Interviews during home visits were used to assess social services and caregiving status for the bedridden and senile elderly living at home in urban Tokyo. In Chuo ward 197 bedridden and senile elderly were identified from 3,409 mailed surveys (response rate 5.8%). This study analyses data from 110 subjects who were followed up with interviews during home visits. As indicated by the Karasawa senile scale, 70% of the respondents have communication problems with the elderly person in their care. Incontinence problems are reported in 56.7% of the frail elderly. There is no significant association between incontinence problems and decisions by caregivers to institutionalize the elderly. The mean age of the main caregiver is 61.9 +/- 12.7 years. There are 55.5% of the families with secondary caregivers. The mean period of care is 6.3 +/- 8.2 years. Even the families who take care of their elderly relative for longer periods of time have no one to consult about caregiving. Caregiver strain was measured by the Family Maslach Burnout Inventory. The subscale, emotional exhaustion, occurs most frequently. Only 25.0% of caregivers indicate willingness to accept social services, on the other hand 63.5% of the caregivers desire family care. The questionnaire listed twenty five resources currently available for families in this ward for social services. Only 52.2% know about resources for social services. Only 8.5% of the respondents use social services. Respondents know about and use social services for direct care of their elderly relative more than they use support for adapting the home environment for the care of the elderly. These findings suggest the following: (1) In order to promote effective use of social services a systematic case finding and assessment plan is needed. (2) Development of services from the viewpoint of prevention and emotional support are needed. (3) Case management is needed to achieve a mix of both the family care and social services.

Aged↗
PubMed1994

Sterol-resistant transcription in CHO cells caused by gene rearrangement that truncates SREBP-2.

Sterol-resistant CHO cells (SRD-1 cells) fail to repress sterol synthesis and LDL receptor gene transcription when incubated with 25-hydroxycholesterol. Here we trace the defect to a rearrangement in the gene encoding SREBP-2, a membrane-bound transcription factor that regulates cholesterol homeostasis. SREBP-2 is an 1139-amino acid protein that is bound to extranuclear membranes via a carboxy-terminal attachment domain. In sterol-depleted cells a protease liberates the amino-terminal fragment (approximately 480 amino acids). This fragment, which contains the transcriptional activation and bHLH-Zip domains, translocates to the nucleus. 25-Hydroxycholesterol abolishes protease activity and halts transcription. SRD-1 cells produce a soluble, truncated form of SREBP-2 (amino acids 1-460) that lacks the membrane attachment domain and activates transcription directly, bypassing the sterol-regulated proteolytic step. Although SRD-1 cells produce full-length SREBP-2 from the wild-type allele and a related transcription factor, SREBP-1, they fail to cleave both of these precursors, indicating that the truncated form of SREBP-2 down-regulates the protease through a form of end-product feedback inhibition. The current data provide genetic evidence for the previously proposed model in which cholesterol homeostasis is controlled by sterol-regulated proteolysis of a membrane-bound bHLH-Zip transcription factor.

Amino Acid Sequence↗
PubMed1994

Modulation of the delayed rectifier K+ current by apamin in guinea-pig heart.

Modulation of the cardiac delayed rectifier K+ current (IK) by apamin was studied in guinea-pig ventricular myocytes using the whole-cell configuration of the patch-clamp technique. Apamin, a peptide toxin isolated from bee venom, is known to inhibit Ca(2+)-activated K+ channel activity. Bath application of apamin prolonged the action potential duration and partially inhibited IK in a concentration-dependent fashion with a half-maximal concentration of 34.4 nM and a Hill coefficient of 1.2. The inhibition of IK occurred at all voltages tested and the block was irreversible. In contrast, the activation curve (P infinity curve) of IK was not shifted by application of apamin, suggesting that the voltage dependence of IK activation is unaffected by apamin. Thus, apamin can partially inhibit cardiac IK without affecting the activation kinetics. This differential sensitivity of IK to apamin suggests that cardiac IK can be separated into two distinct channel populations: the apamin-sensitive K+ channels and the apamin-insensitive K+ channels.

Action Potentials↗
PubMed1994

Assignment of the membrane attachment, DNA binding, and transcriptional activation domains of sterol regulatory element-binding protein-1 (SREBP-1).

Transcription of the low density lipoprotein receptor gene and other sterol-regulated genes is stimulated by sterol regulatory element-binding protein-1 (SREBP-1), a basic-helix-loop-helix-leucine zipper (bHLH-ZIP) transcription factor. Human SREBP-1 is synthesized as an 1147-amino acid precursor that is attached intrinsically to membranes of the nuclear envelope and endoplasmic reticulum. In sterol-depleted cells the precursor is cleaved to generate an NH2-terminal fragment that enters the nucleus and activates transcription by binding to sterol regulatory element-1 (SRE-1). Sterols prevent transcriptional activation by blocking the proteolytic cleavage. In the current studies, performed with hamster SREBP-1, we used mutational analysis to localize the transcriptional activation domain to an acidic NH2-terminal sequence. Deletion of this sequence converted SREBP-1 from an activator to an inhibitor of transcription. DNA binding was assigned to the basic region of the bHLH-ZIP domain. Binding was abolished by substitution of 3 amino acids that were previously implicated in DNA binding by Max, another bHLH-ZIP protein. The membrane attachment domain was localized to two hydrophobic regions at residues 477-497 and 536-556. Truncation of SREBP-1 prior to these regions gave rise to an NH2-terminal fragment that was soluble and entered the nucleus. This fragment was more than 30-fold more active than full-length SREBP-1 in stimulating transcription of an SRE-1 containing reporter gene in transfected cells. Deletion of the hydrophobic sequences (delta 476-556) yielded a protein that appeared cytosolic by immunofluorescence microscopy but failed to enter the nucleus readily, apparently because of inhibition by sequences in the remaining COOH-terminal domain. This study provides a picture of the domain structure of SREBP-1 and further elucidates the mechanism by which it adjusts gene transcription to maintain cholesterol homeostasis in animal cells.

Amino Acid Sequence↗
PubMed1994

Modulation of voltage-dependent inactivation of the inwardly rectifying K+ channel by chloramine-T.

The inwardly rectifying K+ channel (IK1) exhibits voltage-dependent inactivation at membrane voltages more negative than approximately -140 mV. The effect of chloramine-T on the inactivation of IK1 was examined in guinea-pig ventricular myocytes using the patch-clamp technique. Chloramine-T (2 mM) irreversibly inhibited the time-dependent decay of whole-cell IK1 inactivation. As a result, the negative slope region of the current-voltage (I-V) relationship was abolished. In cell-attached single channel recordings, the number of active channels in the patch decreased with time during the voltage-clamp step to the K+ equilibrium potential (EK) of -100 mV. Chloramine-T prevented this time-dependent decrease in channel number, and ensemble averaged currents exhibited abolishment of time-dependent decay of channel activity at EK -100 mV. These results suggest that the hyperpolarization-induced inactivation of cardiac IK1 is controlled by voltage-dependent intrinsic gating.

Animals↗
PubMed1994

SREBP-1, a membrane-bound transcription factor released by sterol-regulated proteolysis.

Sterol regulatory element-binding protein 1 (SREBP-1), a member of the basic-helix-loop-helix-leucine zipper (bHLH-ZIP) family of transcription factors, is synthesized as a 125 kd precursor that is attached to the nuclear envelope and endoplasmic reticulum. In sterol-depleted cells, the membrane-bound precursor is cleaved to generate a soluble NH2-terminal fragment (apparent molecular mass, 68 kd) that translocates to the nucleus. This fragment, which includes the bHLH-ZIP domain, activates transcription of the genes for the LDL receptor and HMG CoA synthase. Sterols inhibit the cleavage of SREBP-1, and the 68 kd nuclear form is rapidly catabolized, thereby reducing transcription. ALLN, an inhibitor of neutral cysteine proteases, blocks the breakdown of the 68 kd form and superinduces sterol-regulated genes. Sterol-regulated proteolysis of a membrane-bound transcription factor provides a novel mechanism by which transcription can be regulated by membrane lipids.

Amino Acid Sequence↗