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S Kurihara

Publications and source records attributed to S Kurihara.

At least 37 records · Page 2Linked to original sources
PubMed2000

Transport of magnesium by two isoforms of the Na+-Ca2+ exchanger expressed in CCL39 fibroblasts.

Cytoplasmic concentrations of Ca2+ ([Ca2+]i) and Mg2+ ([Mg2+]i) were measured with fluorescent indicators in CCL39 cells, a cell line established from Chinese hamster lung fibroblasts, transfected with complementary deoxyribonucleic acid (cDNA) of the Na+-Ca2+ exchanger isolated either from canine heart (NCX1) or from rat brain (NCX3). Raising extracellular [Mg2+] to 10 mM increased Mg2+ influx and the resultant change in [Mg2+]i (delta[Mg2+]i) was monitored with furaptra under Ca2+-free conditions. In control (vector-transfected) cells, delta[Mg2+]i at 45 min was similar with or without extracellular Na+ (130 mM or 0 mM) and when [Na+]i was raised by 1 mM ouabain treatment. delta[Mg2+]i in NCX1-transfected cells was attenuated significantly in the presence of 130 mM Na+, but became comparable to (or slightly larger than) that in control cells on either removal of extracellular Na+ or treatment with 1 mM ouabain. Cells expressing NCX3 showed an intermediate dependence of delta[Mg2+]i on Na+, probably reflecting a lower degree of expression of the exchanger protein. Extracellular Na+-dependent changes in [Ca2+]i (measured with fura-2 in the presence of extracellular Ca2+ and 10 microM ionomycin, a Ca2+ ionophore) were minimal in control cells, marked in the NCX1-transfected cells and intermediate in the NCX3-transfected cells. These results suggest that the Na+-Ca2+ exchanger (either NCX1 or NCX3) can transport Mg2+ and may play a role in the extrusion of magnesium from cells.

Animals↗
PubMed2000

Insulin-like growth factor-I-dependent signal transduction pathways leading to the induction of cell growth and differentiation of human neuroblastoma cell line SH-SY5Y: the roles of MAP kinase pathway and PI 3-kinase pathway.

IGF-I regulates cell growth, differentiation, and survival in many cultured nerve cell lines. The present study was undertaken in the human neuroblastoma cell line, SH-SY5Y, to elucidate whether there are differences in the IGF-dependent signal transduction pathways that stimulate proliferation compared to those that induce differentiation. Quiescent SH-SY5Y cells were treated with IGF-I in the presence or absence of PD98059 (an inhibitor of MEK, a MAP kinase kinase) or LY294002 (an inhibitor of PI 3-kinase). Cell growth was assessed by measuring [3H]thymidine incorporation into DNA and cell number. Cell differentiation was assessed by measuring mRNA levels of NPY and neurite outgrowth. IGF-I both induced cell proliferation and differentiation. It stimulated tyrosine phosphorylation of the type I IGF receptor (IGF-IR) beta-subunit, IRS-I, IRS-2, and Shc, and these changes were associated with activation of Erk and Akt. PD98059 inhibited activation of Erk and LY294002 repressed activation of Akt in response to IGF-I, but did not affect tyrosine phosphorylation of the IGF-IR, IRS-1, IRS-2, or Shc. Each PD98059 and LY294002 inhibited IGF-I-dependent cell proliferation in a concentration-dependent manner. In contrast, each of these inhibitors only partially depressed NPY gene expression induced by IGF-I and slightly inhibited IGF-I-mediated neurite outgrowth; however, when both PD98059 and LY294002 were present, IGF-I-dependent NPY gene expression and neurite outgrowth were abolished completely. These results suggest that in these nerve cells, 1) the IGF-I signals through the MAP kinase pathway and PI-3 kinase pathway are independently essential to induce IGF-I-dependent growth, and 2) alternate activation of the MAP kinase pathway and PI 3-kinase pathway is sufficient for the cells to undergo IGF-I-dependent differentiation.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Logistic time constant of isometric relaxation force curve of ferret ventricular papillary muscle: reliable index of lusitropism.

We have found that a logistic function fits the left ventricular isovolumic relaxation pressure curve in the canine excised, cross-circulated heart more precisely than a monoexponential function. On this basis, we have proposed a logistic time constant (tau(L)) as a better index of ventricular isovolumic lusitropism than the conventional monoexponential time constant (tau(E)). We hypothesize in the present study that this tau(L) would also be a better index of myocardial isometric lusitropism than the conventional tau(E). We tested this hypothesis by analyzing the isometric relaxation force curve of 114 twitches of eight ferret isolated right ventricular papillary muscles. The muscle length was changed between 82 and 100% L(max) and extracellular Ca(2+) concentrations ([Ca(2+)](o)) between 0.2 and 8 mmol/l. We found that the logistic function always fitted the isometric relaxation force curve much more precisely than the monoexponential function at any muscle length and [Ca(2+)](o) level. We also found that tau(L) was independent of the choice of the end of isometric relaxation but tau(E) was considerably dependent on it as in ventricular relaxation. These results validated our present hypothesis. We conclude that tau(L) is a more reliable, though still empirical, index of lusitropism than conventional tau(E) in the myocardium as in the ventricle.

Animals↗
PubMed2000

Effects of "isolating hemodialysis" on prevention of methicillin-resistant Staphylococcus aureus cross-infection in a hemodialysis unit.

AIM: To evaluate the effects of a contact isolation program against methicillin-resistant Staphylococcus aureus (MRSA) cross-infection among patients in a hemodialysis unit. CLINICAL SETTING AND METHODS: In all patients maintaining hemodialysis therapy were tested for MRSA infection and who had MRSA infection, not only inpatients but also outpatients were separated into a designated area (isolating hemodialysis). Clinically isolated MRSA strains were clonotyped with coagulase typing, staphylococcal enterotoxin typing and restriction enzyme analysis of plasmid DNA. RESULTS: The frequency of patients with MRSA infection was 4.5% before starting this protocol and was reduced to 2.9% two and a half years later. At this time, MRSA was isolated from the 8 patients. These 8 clinical strains were differentiated into 6 clonotypes and 3 strains showed the same patterns. Two of 3 were isolated from inpatients and the other was from a patient with community onset MRSA colitis. In this case, most MRSA infections were independent under prophylaxis control and cross-infection was observed only once between hospitalized patients who stayed in a same ward. CONCLUSION: This "isolating hemodialysis" should be useful to prevent cross-infection among patients in end-stage renal disease in a dialysis unit.

Adult↗
PubMed2000

Clonotypes of Staphylococcus aureus isolated from continuous ambulatory peritoneal dialysis patients: what is the vector between nares and infection site?

Staphylococcus aureus is frequently isolated from patients with infections related to continuous ambulatory peritoneal dialysis (CAPD). In many cases, the organism is also isolated simultaneously from the anterior nares. To clarify the transmission trail of S. aureus, we used DNA analysis to identify clonotypes of clinical strains. The nares and exit sites of 32 CAPD patients were swabbed, and PD fluid samples were taken for pathogen culture. Genome DNA of S. aureus was digested with restriction enzyme Sma I for pulsed-field gel electrophoresis. We also asked the patients how they usually performed the PD procedure. S. aureus was isolated from 4 patients, including 3 who hosted two strains isolated separately from different sites. The DNA patterns of the strains isolated from these latter 3 patients were identical. However, the clonotypes from all 4 patients were different. Most of the patients did not wash their hands and wear masks while exchanging PD bags and caring for their exit sites. After the patients were disinfected and re-educated in proper procedures, S. aureus was not detected in any of them. These data suggest that no outbreak occurred in our hospital and that the vectors of endogenous infection were the patients themselves, probably their hands. A bacteriological study presents an efficient opportunity to re-educate patients in PD procedure.

Adult↗
PubMed1999

Modulation of Ca2+ transient decay by tension and Ca2+ removal in hyperthyroid myocardium.

We investigated the contribution of sarcoplasmic reticulum (SR) and Na+/Ca2+ exchanger in the tension-dependent change in the decay of the Ca2+ transients (CaT) in euthyroid (Eu) and hyperthyroid (Hy) myocardium. Hy was induced by thyroxine treatment to enhance the rate of SR Ca2+ uptake. With the use of the aequorin method, CaT and tension in twitch contraction were simultaneously measured under various conditions (changing muscle length and Ca2+ concentration in solution). In both groups, the decay time of CaT (DT) showed a significant dependence on the developed tension, but the tension dependence of DT in Hy was significantly less than in Eu. In the presence of caffeine (3 mM), the tension dependence of DT in Hy became apparent as in Eu. Inhibition of Na+/Ca2+ exchanger by replacing Na+ with Li+ did not affect the dependence in Hy. The normalized extra Ca2+, which is the Ca2+ concentration change in response to a quick length change, in Hy was similar to that in Eu. pCa-tension relations of skinned trabeculae measured at different lengths (1.9 and 2.3 micrometer) were nearly identical in both groups. These results indicate that the tension-dependent change in the affinity of troponin C for Ca2+ works in both Eu and Hy myocardium and that the tension-dependent change in DT is influenced by the Ca2+ uptake rate of SR.

Animals↗
PubMed1999

Alterations in contractile properties and Ca2+ handling in streptozotocin-induced diabetic rat myocardium.

The mechanisms of the slower time courses of Ca2+ transients (CaT) and contraction in diabetic (diabetes mellitus, DM) myocardium were studied. The aequorin method was applied to papillary muscles of streptozotocin-induced DM and control rats. The time courses of CaT and tension of twitch in DM were slower than those in control, although the magnitudes of the CaT and contraction were identical. The dependence of CaT decay time and relaxation time on developed tension in DM and control rats differed. The length-tension relation in twitch and the pCa-tension relation in tetanus were identical in the two groups. The magnitude of extra Ca2+ (transient increase in intracellular Ca2+ concentration induced by a quick release in tetanus) was identical in both groups. pCa-tension relations of skinned trabeculae at different sarcomere lengths were nearly identical. The cross-bridge cycling rate (CCR) in DM was slower than that in control. These results indicate that the tension-dependent change in the Ca2+ affinity of troponin C in DM myocardium functions as in control myocardium. The slower time courses of CaT and tension in DM myocardium are caused by slower Ca2+ uptake by the sarcoplasmic reticulum and the slower CCR.

Animals↗
PubMed1999

Pentanucleotide repeat and size polymorphisms in the apolipoprotein(a) gene are associated with the lipoprotein(a) concentration in chronic hemodialysis patients.

The elevation of serum or plasma lipoprotein(a) [Lp(a)] levels is regarded as an independent risk factor for cardiovascular disease, and many previous reports demonstrated that Lp(a) levels in hemodialysis patients were significantly higher than in controls. The purpose of this study was to investigate the effect of a pentanucleotide repeat polymorphism [(TTTTA)n] in the 5'-flanking region of the apolipoprotein(a) [apo(a)] gene and of a size polymorphism of apo(a) for elevated Lp(a) concentrations observed in chronic hemodialysis patients. We studied 172 patients on chronic hemodialysis and 199 healthy adults. For analysis of the pentanucleotide repeat polymorphism, polymerase chain reaction products were loaded on polyacrylamide gel for electrophoresis. apo(a) size phenotyping was performed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The median level of Lp(a) in the patients was 14.2 mg/dl which was significantly higher than that in controls (12.0 mg/dl; p < 0.05). In the genotype of (TTTTA)8/8, the median Lp(a) level in the patients (15.9 mg/dl) was significantly higher than that in controls (13.0 mg/dl; p < 0.05). In the genotype of (TTTTA)8/8 with large-sized apo(a) isoforms (A16-A25), the patients had significantly higher Lp(a) levels than the controls (p < 0.05). In conclusion, increased Lp(a) levels in chronic hemodialysis patients were mainly attributed to the combination of eight repeats of the pentanucleotide polymorphism and large-sized isoforms of apo(a).

Apolipoproteins A↗
PubMed1999

Hypercalcemia accompanied by hypothalamic hypopituitarism, central diabetes inspidus and hyperthyroidism.

We present here a case of prominent hypercalcemia accompanied by hypothalamic tumor and Graves' disease. A 24-year-old man with hypothalamic tumor showed hypopituitarism, central diabetes inspidus (DI) and hyperthyroidism. Nausea, loss of thirst and appetite, and general fatigue were found with the unveiling of hypercalcemia and hypernatremia. Parathyroid hormone (PTH) and 1alpha-dihydroxyvitamin D levels were suppressed with a normal range of PTH-related protein values. One-desamino-(8-D-arginine)-vasopressin (DDAVP) and half-saline administration normalized hypernatremia, while hypercalcemia was still sustained. Administration of cortisone acetate and thiamazole reduced the elevated serum Ca level. In the present case, concurrent hyperthyroidism was assumed to accelerate skeletal mobilization of calcium into the circulation. Hypocortisolism and central DI was also considered to contribute, to some extent, to the hypercalcemia through renal handling of Ca.

Adult↗
PubMed1999

Hybrid logistic characterization of isometric twitch force curve of isolated ferret right ventricular papillary muscle.

We previously found that the isovolumic pressure curve of the left ventricle and the isometric twitch force curve of the right ventricular in situ papillary muscle, both of the blood-perfused canine heart, were precisely fitted by our newly proposed hybrid logistic function. This function describes the difference between the two S-shaped logistic functions for the rising and falling components: A/[1+exp{-(4B/A)(t-C)}]-D/[1+exp{-(4E/D)(t-F)}]+G. This function characterizes comprehensively both ventricular and in situ papillary muscle contraction and relaxation. In the present study, we hypothesized that this function could also characterize the force curve of the most popular, standard-type, isolated and Tyrode-superfused papillary muscle preparation. To test this hypothesis, we investigated how precisely the hybrid logistic function could fit 112 isometric twitch force curves observed in eight isolated and Tyrode-superfused ferret right ventricular papillary muscles at different muscle lengths and extracellular Ca2+ concentrations. We always obtained a precise curve fitting with a correlation coefficient above 0.9987. This fitting was much more precise than sinusoidal and polynomial exponential function curve fittings. These results supported the present hypothesis. We conclude that our hybrid logistic function reasonably characterizes the force curve of the isolated myocardial preparation. This result broadens the generality of the hybrid logistic characterization of ventricular isovolumic pressure and myocardial isometric twitch force generation. The hybrid logistic characterization seems to be an integrative expression of contractile processes in myocardial twitch contraction.

Animals↗
PubMed1999

[A case of interstitial nephritis induced by a super antigen produced by methicillin-resistant Staphylococcus aureus (MRSA) presenting as acute renal failure].

We report the case of a 21-year-old man who had been developing acute renal failure with Methicillin-resistant Staphylococcus aureus (MRSA) colitis and sepsis. He was admitted for consciousness disturbance, nausea, vomiting, and diarrhea. Oliguria was also observed and his serum creatinine level was elevated to 10 mg/dl. Urinary protein was positive and an abundance of hyaline cast were seen in urinary sedimentation. Diarrhea and pyrexia were prolonged and serum C-reactive proteins were elevated, but lymphocyte and leukocyte counts temporarily decreased from the 3rd to the 6th hospital day and remained low until normalizing after the 14th day. His clinical symptoms improved with hemodialysis (HD) and effective antibiotic therapies. An MRSA strain producing toxic shock syndrome toxin-1 (TSST-1), a super antigen which specifically stimulates human V beta 2-positive T cells, was separated from his feces and blood. To ascertain the cause of his renal dysfunction, a renal biopsy was performed on the 8th day. His renal histology revealed acute interstitial nephritis with severe inflammatory cell infiltration around the medullary areas without glomerular changes. Most of the infiltrated cells were small monocytes, and lymphoid cells were rich in the interstitium. With immunohistochemical staining, over 70% of T-cells were V beta 2-positive. TSST-1-producing MRSA was detected in his blood specimen. Furthermore, V beta 2-positive T cells were accumulated in the renal intersititium, and transient lymphocytopenia was observed. These data suggested the following possible pathogenesis for interstitial nephritis: TSST-1 acts as a super antigen in the renal interstitium where major histocompatibility complex (MHC) is class-2-positive, thereby resulting in interstitial nephritis with T cell migration.

Acute Kidney Injury↗
PubMed1999

Changes in body fluid distribution during 7 days 6 degrees head-down bed rest.

It is well known that, in a state of weightlessness, body fluids shift toward the head site, but the actual rates of the migration of fluids has never been measured. In order to identify the causes of reduced orthostatic tolerance and the reduction in circulating blood volume after returning from a space mission, it is necessary to measure the changes in body fluid distribution. Although the methods for measuring changes in body fluids include the use of isotopes or pigments, such methods cannot be employed in space due to their invasive properties. Therefore, we directed our attention toward the impedance method, for which we developed a non-invasive apparatus for measuring the distribution of body fluids. We therefore measured the actual distribution of body fluids using the bed-rest method, a model of the zero gravity state.

Abdomen↗
PubMed1998

Estimation of myofibrillar responsiveness to Ca2+ in isolated rat ventricular myocytes.

To estimate myofibrillar responsiveness to Ca2+, we used the relation between cell length and intracellular [Ca2+] ([Ca2+]i) during tetanic contractions of isolated ventricular myocytes. Enzymatically isolated rat ventricular myocytes were loaded with fura-2 AM (4 microM for 10 min) and excited alternately at 340 nm and 380 nm. The ratio (R) of fura-2 fluorescence at these wavelengths [F(340)/F(380), an index of [Ca2+]i] and cell length (L) were measured simultaneously. Following treatment with thapsigargin (0.2 microM), myocytes were stimulated at 10 Hz for 10 s to produce a tetanic contraction every min and an instantaneous plot of R vs L (R-L trajectory) was constructed. The R-L trajectory followed the same path during cell shortening and re-lengthening, suggesting that dynamic equilibrium between R and L was achieved during tetanus. Increasing the extracellular [Ca2+] from 1 to 8 mM extended the R-L trajectory without a substantial shift of the relation. The Ca2+-sensitizing thiadiazinone derivative, EMD57033 (1 microM), shifted the R-L trajectory to the left (sensitization of the myofibrils to Ca2+), whereas the non-selective phosphodiesterase inhibitor, 3-isobutyl-1-methylxantine (200 microM), shifted the R-L trajectory to the right (desensitization of the myofibrils to Ca2+), in agreement with previous results obtained using skinned preparations. We conclude that the R-L trajectory is useful for estimating the myofibrillar responsiveness to Ca2+ in isolated myocytes and may be beneficial for the evaluation of inotropic agents.

1-Methyl-3-isobutylxanthine↗
PubMed1998

Insertion/deletion polymorphism in intron 16 of the ACE gene and left ventricular hypertrophy in patients with end-stage renal disease.

We studied the relationship between polymorphism in intron 16 of the angiotensin-converting enzyme (ACE) gene and left ventricular (LV) hypertrophy in uremic patients treated with hemodialysis therapy. The LV parameters were not different for age-, hematocrit-, and blood pressure-matched patients in DD, ID, and II genotype groups. The most important factor for LV hypertrophy was systolic blood pressure, which correlated with the posterior wall thickness (r=0.35; P=0.001) and LV mass index (LVMI; r=0.23; P=0.032). Among nonhypertensive patients, the frequency of interventricular septum (IVS) hypertrophy (>12 mm) and hypertrophy in LVMI (>145 g/m2) was significantly greater in patients with the DD genotype than in I allele-positive (+) patients. The odds rate for IVS hypertrophy was 5.04 (95% confidence interval, 1.15 to 24.8). These data suggest that the DD genotype of the ACE gene polymorphism is a contributory factor for the development of LV hypertrophy in patients with end-stage renal disease (ESRD).

Age Factors↗
PubMed1998

Controlled trial of falecalcitriol versus alfacalcidol in suppression of parathyroid hormone in hemodialysis patients with secondary hyperparathyroidism.

Active vitamin D3 is extensively used for the treatment of secondary hyperparathyroidism in hemodialysis patients. But it is often impossible to administer enough dose to suppress parathyroid hormone (PTH) level, because of hypercalcemia and hyperphosphatemia. New modalities with higher specificity for PTH suppression are desirable. We conducted a crossover comparative study of falecalcitriol, an active vitamin D3 analog, and alfacalcidol (1alpha[OH]D3). In this study, 25 hemodialysis patients with moderate to severe secondary hyperparathyroidism who had normal serum calcium levels were enrolled. They received daily oral doses of alfacalcidol during an 8-week observation period. Based on serum calcium levels and intact PTH, the subjects were allocated into two groups, and a comparative study was conducted using unmasked crossover design of two drugs x two periods. The dosage of both drugs was adjusted to maintain the initial serum calcium levels, and the relative change (%change) of serum biochemical parameters were compared. Comparison of two drugs in period 1 was taken as primary efficacy evaluation. Reproducibility of drug action was confirmed by comparing the effect of falecalcitriol between period 1 and 2. The percent change of PTH of falecalcitriol was lower than that of alfacalcidol: Those were, respectively, -7.89% and +30.42% for c-terminal PTH (P = 0.022), -4.39% and +38.88% for i-PTH (P = 0.077), and +3.68% and +30.52% for midregion PTH (P = 0.099). The similar changes were observed in the falecalcitriol group during period 2, confirming the reproducibility. Falecalcitriol was found to be superior to alfacalcidol in suppression of PTH levels in patients with moderate to severe secondary hyperparathyroidism when it is administered in equivalent doses that might maintain similar serum calcium levels.

Adult↗
PubMed1998

Effects of acidosis on Ca2+ sensitivity of contractile elements in intact ferret myocardium.

We investigated the effects of acidosis on the intracellular Ca2+ concentration ([Ca2+]i) and contractile properties of intact mammalian cardiac muscle during tetanic and twitch contractions. Aequorin was injected into ferret papillary muscles, and the [Ca2+]i and tension were simultaneously measured. Acidosis was attained by increasing the CO2 concentration in the bicarbonate (20 mM)-buffered Tyrode solution from 5% (pH 7.35, control) to 15% (pH 6.89, acidosis). Tetanic contraction was produced by repetitive stimulation of the preparation following treatment with 5 microM ryanodine. The relationship between [Ca2+]i and tension was measured 6 s after the onset of the stimulation and was fitted using the Hill equation. Acidosis decreased the maximal tension to 81 +/- 2% of the control and shifted the [Ca2+]i-tension relationship to the right by 0.18 +/- 0.01 pCa units. During twitch contraction, a quick shortening of muscle length from the length at which developed tension became maximal (Lmax) to 92% Lmax produced a transient change in the [Ca2+]i (extra Ca2+). The magnitude of the extra Ca2+ was dependent on the [Ca2+]i immediately before the length change, suggesting that the extra Ca2+ is related to the amount of troponin-Ca complex. Acidosis decreased the normalized extra Ca2+ to [Ca2+]i immediately before the length change, which indicates that the amount of Ca2+ bound to troponin C is less when [Ca2+]i is the same as in the control. The decrease in the Ca2+ binding to troponin C explains the decrease in tetanic and twitch contraction, and mechanical stress applied to the preparation induced less [Ca2+]i change in acidosis.

Acidosis↗
PubMed1998

Dynamic relations among length, tension, and intracellular Ca2+ in activated ferret papillary muscles.

To study the effects of mechanical constraints on the Ca2+ affinity of cardiac troponin C, we analyzed the tension and aequorin light (AL) responses to sinusoidal length changes (5-10% of the initial muscle length) in aequorin-injected, tetanized cardiac muscles. The amplitude of the quasi-sinusoidal tension and AL responses decreased with increasing length-perturbation frequency from 0.5 to 1 Hz at 24 degreesC and from 1 to 3 Hz at 30 degreesC. The increase in AL corresponded well to the decrease in tension; likewise, the decrease in AL to the increase in tension and the tension response lagged behind the length change. A further increase in frequency (>1 Hz at 24 degreesC and >3 Hz at 30 degreesC) markedly increased the amplitude of the tension responses but decreased the amplitude of the AL responses. The increase in AL lagged behind the decrease in tension; likewise, the decrease in AL lagged behind the increase in tension, and the tension response led the length change. From previous mechanistic interpretations of the frequency dependence of the amplitude of tension response, we argue that the Ca2+ affinity of cardiac troponin C changes in parallel with the active tension (i.e., the number of active cross bridges) but not with the passive tension produced by the length perturbation-induced cross-bridge strain.

Aequorin↗