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K Kamiya

Publications and source records attributed to K Kamiya.

At least 145 records · Page 8Linked to original sources
PubMed1996

Effects of chronic hypoxia on the developmental changes in action potential of cultured neonatal rat ventricular myocytes.

The action potentials of rat ventricular myocytes are known to become progressively shortened within several weeks after birth. We studied the effects of long-term exposure to hypoxia on these developmental changes in cardiac action potentials. Single ventricular myocytes isolated from day-old neonatal rat hearts were cultured in normoxic conditions (21% O2) for more than 15 days. To test the influence of long-term exposure to hypoxia, O2 tension was lowered to 7.5% in some cells at day 6. Action potentials were measured at day 5 and day 15 in both the normoxic and hypoxic groups. Under normoxic conditions, action potential durations decreased by 44% between day 5 and day 15, while cell capacitance doubled (n=10-11). Under hypoxic conditions, action potential durations decreased slightly by 16% (n=6). This shortening was significantly attenuated when compared to that observed during normoxic conditions. Cell capacitance was not altered under the hypoxic conditions. These results suggest that 1) shortening of the action potential during normoxic culturing is prevented under hypoxic conditions, and 2) cell capacitance as seen in normoxic conditions is unaffected by hypoxic culturing.

Action Potentials↗
PubMed1996

[Analysis of the iron-related proteins during proliferation and differentiational change of human hepatoblastoma cells (HepG2)].

The modulation of cellular iron metabolism depends on the expression of ferritin and transferrin receptor (TfR). These proteins are regulated post-transcriptionally by interaction of specific sequences, termed iron responsive elements (IRE) which are located in the 5' untranslated region (UTR) of ferritin mRNA and 3'UTR of TfR mRNA and a specific cytosolic protein, termed iron responsive element-binding protein (IRE-BP). The liver plays an important role in iron metabolism as a major organ of iron storage. In hepatocytes iron is taken up in the form of transferrin and intercellular iron levels are regulated by IRE/IRE-BP interaction. In spite of the important role of IRE/IRE-BP interaction, the role of it for proliferation and differentiational change in hepatoma cells is not well known. In this study, the author has investigated IRE/IRE-BP interaction and its target protein expression during proliferation and differentiational change of human hepatoblastoma cells (HepG2). This study revealed that the binding activity of IRE-BP to IRE was increased when HepG2 cells were cultured with an iron-chelating agent, deferoxamine (4.5 microM), and it was decreased when cultured with transferrin (100 micrograms/ml) during both proliferation and differentiational change induced by sodium butyrate. Also, the change of TfR expression was correlated with that of IRE-BP. These findings suggest that IRE/IRE-BP interaction may play an important role in the expression of TfR and cellular iron metabolism during proliferation and differentiational change of HepG2 cells.

Base Sequence↗
PubMed1996

Differential effects of MS-551 and E-4031 on action potentials and the delayed rectifier K+ current in rabbit ventricular myocytes.

OBJECTIVE: The frequency-dependent effects of MS-551 on the action potential duration (APD) and the underlying ionic mechanisms were investigated in comparison with those of E-4031. METHODS: Whole-cell clamp techniques were used to study action potentials and ionic currents in enzymatically isolated rabbit ventricular myocytes. RESULTS: The frequency-response obtained within the range of 0.1 to 3.3 Hz was different for MS-551 and E-4031. The APD prolongation by MS-551 (10 microM) was significant at 0.5-3.3 Hz, whereas that by E-4031 (1 microM) was significant at 0.1-1.0 Hz. The prolongation by MS-551 (10 microM) of APD of a test action potential, which was preceded by a train of 1.0 Hz stimulation, decreased progressively as the rest duration increased, whereas that by E-4031 (1 microM) remained at the same level. Both MS-551 (10 microM) and E-4031 (1 microM) significantly decreased IK, but showed no effects on the transient outward current (Ito) and the inward rectifier K+ current (IKl). The development of the block on IK and the recovery from the block by MS-551 were voltage dependent. At a holding potential of -50 mV, MS-551 reduced the tail current to a similar extent (21-34%, n = 6) across all the tested durations of the depolarizing pulses to +10 mV, whereas at -75 mV, the intensity of the block progressively increased as the durations of depolarizing pulses were prolonged. The recovery from the block by MS-551 was absent at -50 mV, but occurred at -75 mV with a time constant of 577 +/- 179 ms (n = 6). The development of the block on IK by E-4031 was voltage and time independent. No recovery from the block was observed for E-4031 at either -50 or -75 mV. CONCLUSIONS: These findings suggest that MS-551 produces frequency-dependent class III action, presumably due to the voltage-dependent binding and unbinding to the IK channels. The reverse frequency dependence of class III action by E-4031 cannot be explained by the effects on IK.

Action Potentials↗
PubMed1996

[Reconstruction of the crural artery in atherosclerotic occlusive arterial disease].

Limb threatening ischemia in patients with atherosclerotic occlusive disease is frequently induced by the association of crural artery occlusion. To improve the patency of distal bypass grafts, we developed a "non-dissection method" for reconstruction of these lesions. This method involves following procedures; an adventitial dissection limited to the frontal surface of the artery at the anastomotic site, complete evacuation of blood from the lower leg using a Esmarch's rubber bandage or a pneumatic tourniquet under systemic heparinization, and distal anastomosis with vein graft in end to side fashion with long arteriotomy (20 mm in length) without use of vascular clamps. This method has several advantages to the conventional method, such as easiness of suturing for accurate anastomosis, preservation of the muscular branches around the anastomosis, avoidance of surgery-induced injury to the artery and prevention of postoperative cicatrization around the anastomosis which may affect natural enlargement of the bypassed native artery. The technical details are described. Since 1982, 76 tibial bypass surgeries were performed using this method. Whenever stenotic lesions were recognized, the grafts were revised and counted as a primary occlusion. The primary patency rates at 1 year, 3 years, 5 years and 10 years are 82.2%. 75.8%, 63.9% and 63.9% respectively. The secondary patency rates are 89.1%, 84.8%, 80.8% and 80.8% respectively at the same term.

Arterial Occlusive Diseases↗
PubMed1996

Superior cytotoxic potency of mitoxantrone in interaction with DNA: comparison with that of daunorubicin.

The mechanism of action of the anthraquinone antileukemic drug mitoxantrone (MIT) was investigated and compared with that of daunorubicin (DNR) with emphasis on the interaction with DNA to clarify the more potent cytotoxic activity of MIT than DNR in human leukemia cells. MIT showed similar characteristics to those of the anthracyclines such as DNR in that binding of MIT to DNA was associated with reduced template activity and cleavage of DNA in HL-60 human leukemia cells. However, as compared with DNR, MIT showed an increased number of binding sites on DNA, a lower inhibition constant for DNA polymerization, and a greater DNA cleavage activity. These properties may contribute to its greater potency than that of DNR, with which MIT inhibited the proliferation of HL-60 human leukemia cells.

Antineoplastic Agents↗
PubMed1996

Modulated expression of transient outward current in cultured neonatal rat ventricular myocytes: comparison with development in situ.

OBJECTIVES: Developmental changes of cardiac ion channels have been characterized in freshly isolated mammalian heart cells. To investigate the regulatory factors of postnatal development in transient outward current (Ito) in cardiomyocytes, the modulated expression of Ito was studied in cultured neonatal rat ventricular cells. These changes in vitro were compared with those in situ in acutely isolated ventricular myocytes. METHODS: Ventricular cells were enzymatically isolated from day-old Wistar rats and cultured under various growth conditions from day 6 to 15. Whole-cell patch-clamp recording was used to study the functional expression of Ito. RESULTS: During development in situ from 5- to 15-day-old stages, Ito density was doubled at day 15 with a significant increase in membrane capacitance (Cm) of the myocytes. Some cells were incubated in serum-rich medium from day 6 to 15 during primary culture, revealing marked increases in both Cm and Ito density at day 15. However, no developmental changes in the Cm and Ito density were observed in serum-free medium. Under the serum-free condition, neither the addition of acidic fibroblast growth factor (aFGF) nor basic FGF (bFGF) to culture medium influenced the Cm. aFGF (10-60 ng/ml) failed to stimulate Ito expression. 72-h treatment with bFGF significantly promoted the Ito density in a concentration-dependent manner; nevertheless, prolonged administration from day 6 to 15 did not induce a further increase, resulting in lower Ito density than in age-matched freshly isolated and serum-treated preparations. The increase in Ito in cultured cells induced by serum and bFGF may be attributable to paralleling changes in the ionic selectivity of the channel, but was not caused by changes in the voltage-dependence of steady-state Ito activation and inactivation. CONCLUSIONS: bFGF and some other unknown serum factors may play important roles in the postnatal expression of Ito in the neonatal cardiomyocytes. The developmental increase in Ito and postnatal cell hypertrophy of neonatal cardiomyocytes can be regulated independently.

Animals↗
PubMed1995

Association of minisatellite instability with c-myc amplification and K-ras mutation in methylcholanthrene-induced mouse sarcomas.

Instability of microsatellite sequences are frequently found in human tumors. In addition, minisatellite sequences, another group of highly unstable sequences, serve as sensitive markers of genetic instability. We have studied minisatellite instability in methylcholanthrene-induced mouse sarcomas. These sarcomas frequently carry the amplified c-myc gene. Seven sarcomas without the amplification and seven others with the amplification were selected randomly. Regardless of the state of the c-myc gene amplification, these sarcomas exhibited a varying degree of transplantability in syngeneic mice. The hypervariable mouse minisatellite locus Ms6hm was found to be highly unstable, specifically among sarcomas with the amplified c-myc gene. However, chromosome instability, as analyzed by micronucleus assay, was observed similarly for two groups of sarcomas. In addition, transversion of G to C and A to T was detected at the K-ras gene in four of the seven sarcomas with the amplified c-myc gene, and these mutations are thought to be induced directly by methylcholanthrene. Thus, concomitant occurrence was observed for three seemingly unrelated mutations, amplification of the c-myc locus, point mutation of the K-ras gene, and instability at the hypervariable mouse minisatellite locus. The present study indicates a possible involvement of K-ras mutation and c-myc amplification in induction of genetic instability in methylcholanthrene-induced mouse sarcomas.

Animals↗
PubMed1995

Evidence that carcinogenesis involves an imbalance between epigenetic high-frequency initiation and suppression of promotion.

Evidence is presented in support of the hypothesis that cancer development depends on an imbalance between highly frequent epigenetic initiation and suppression of promotion of the initiated cells. When irradiated clonogenic mammary epithelial cells are transplanted and hormonally stimulated, they give rise to clonal glandular structures within which carcinomas may arise. In the current study, the cancer incidence in grafts of approximately 13 7-Gy-irradiated clonogens per site indicated that at least 1 of approximately 95 clonogens was radiogenically initiated. A similar initiation frequency had been seen in grafts of approximately 5 methylnitrosourea (MNU)-treated clonogens. Such initiation is thus far more frequent than specific locus mutations. In sites grafted with larger cell inocula, cancer incidences per clonogen were suppressed inversely as the numbers of irradiated or MNU-treated clonogens per graft increased. Addition of unirradiated cells to small irradiated graft inocula also suppressed progression. Radiation and MNU thus produce quantitatively, and perhaps qualitatively, similar carcinogenesis-related sequelae in mammary clonogens.

Adenocarcinoma↗
PubMed1995

Collateral artery bypass in Buerger's disease: report of a novel procedure.

A 25-year-old man was admitted to our hospital for treatment of a painful ulcer on his left fourth toe, 9 years after undergoing lumbar sympathectomy and 4 years after undergoing bypass, both of which had been unsuccessful. Angiography demonstrated diffuse arterial occlusion in the lower extremities except for a persistent sciatic artery and a sural artery, which was the main collateral. Thus, reversed bifurcated saphenous vein bypass from the sciatic artery to the sural artery and the posterior tibial artery was performed utilizing Esmarch's rubber bandage as a substitute for a vascular clamp to control bleeding intraoperatively. The ulcer healed promptly and the patient was discharged symptom-free 1 month postoperatively. This case report demonstrates the advantage of performing collateral arterial bypass and illustrates some of the technical challenges associated with this procedure.

Adult↗
PubMed1995

Rupture of an isolated internal iliac artery aneurysm into the rectum: report of a case.

Aneurysmal rupture into the intestinal tract is a rare but disastrous complication of an internal iliac artery aneurysm. We report herein the successful surgical repair of a fistula between a huge aneurysm of the right internal iliac artery and the rectum in an 81-year-old man. After a femoro-femoral cross-over bypass had been performed, the aneurysm was opened and its patent arterial branches were ligated with sutures. The fistula was then intra-aneurysmally sutured and covered with an omental flap. The diagnostic and therapeutic approaches to this severe complication are discussed with a review of the literature following the presentation of this case.

Aged↗
PubMed1995

bFGF promotes functional expression of transient outward currents in cultured neonatal rat ventricular cells.

To investigate the effect of basic fibroblast growth factor (bFGF) on ion channel expressions in developing cardiac cells, a short-term primary culture of ventricular myocytes isolated from day-old newborn rats was established. Functional expressions of the transient outward currents (Ito) were measured by whole-cell voltage-clamp method. Addition of 40 ng/ml bFGF to the serum-free culture medium for 72 hours increased the Ito density without influences on membrane capacitance of the myocytes, an estimate of cell size. bFGF also promoted expressions of the steady-state outward currents. Methyl 2,5-dihydroxycinnamate (3 microM), a tyrosine kinase inhibitor, showed preferential inhibition of the bFGF-stimulated increase in Ito density. These results suggest that bFGF may play a role in regulating ion channel expressions of developing cardiac cells via activation of bFGF receptor tyrosine kinase activity.

Animals↗
PubMed1995

A case of spinal low-grade astrocytoma with exophytic and intracranial extension.

BACKGROUND: Ventral exophytic growth of a spinal intramedullary glioma into the cranial cavity is an unusual condition. CASE DESCRIPTION: A 16-year-old boy was admitted because of lower cranial nerve dysfunction and acute hydrocephalus. Magnetic resonance images showed an intramedullary mass lesion in the upper cervical spinal cord with exophytic extension into the medullary and prepontine cisterns. The patient underwent suboccipital craniectomy and C1-2 laminectomy for decompression and histologic evaluation. The histopathologic findings were characteristic of astrocytoma grade II. Although radiotherapy was performed, the patient died 7 months later. CONCLUSIONS: This is considered to be a rare case of spinal low-grade astrocytoma with ventral exophytic intracranial extension.

Adolescent↗
PubMed1995

Radiation-induced apoptotic cell death in human gastric epithelial tumour cells; correlation between mitotic death and apoptosis.

The mode of cell death in cells undergoing mitotic death after gamma-irradiation was studied in seven human gastric epithelial tumour cell lines and two strains of normal gastric fibroblasts. Apoptotic cells were frequently observed in all tumour lines after irradiation, whereas the two fibroblast strains were quite low in apoptosis frequency. The advent of apoptosis depended on the radiation doses and incubation time. Detailed analysis of one of the carcinoma lines, SH101-P4, revealed that G2-phase arrest was maximum at 12 h postirradiation. The cells began to escape G2 arrest by 24 h. Apoptotic cells began to increase at 12 h postirradiation and became maximal from 72 to 96 h. Apoptosis developed in the G1 phase of the cell cycle subsequent to the irradiation. These results suggest that apoptosis is one of the modes of mitotic death after irradiation.

Adenocarcinoma↗
PubMed1995

Dose-response of a radiation induction of a germline mutation at a hypervariable mouse minisatellite locus.

Dose-response of an induction of a germline mutation was studied at a hypervariable mouse minisatellite locus, Ms6hm, which consists of tandem repeats of a sequence motif GGGCA. Male C3H/HeN mice were exposed to various doses of 60Co gamma-ray and mated with unirradiated C57BL/6N female mice. Matings were done at various time after irradiation to assess the effects of radiation on spermatozoa, spermatids and spermatogonia. DNA samples of F1 offsprings were analysed by Southern blotting for the repeat length mutation at the Ms6hm locus. The mutation frequency per gamete of the paternal allele was 9.1% for the unirradiated control group. The spermatids stage was most sensitive to radiation and a statistically significant dose-response was observed. The mutation frequency of the paternal allele in F1 mice increased to 22% for 1 Gy, 28% for 2 Gy, and 28% for 3 Gy. The spermatogonia stage was less sensitive to radiation, and the mutation frequencies of the paternal allele were 14% for 2 Gy, and 16% for 3 Gy. The spermatozoa stage germ cells were also less sensitive and the frequency of mutation of the paternal allele increased to 14% for 3 Gy. However, these increases were statistically not significant. Possible mechanisms of radiation induction of germline mutation at the hypervariable minisatellite locus will be discussed.

Alleles↗
PubMed1995

Over-expressed ZF5 gene product, a c-myc-binding protein related to GL1-Kruppel protein, has a growth-suppressive activity in mouse cell lines.

ZF5 encodes a zinc finger protein, which contains five C2H2-type zinc fingers showing homology with the zinc finger of the Kruppel family, and binds to two sites in the mouse c-myc promoter. We report the effect of over-expression of ZF5 on cell growth. ZnCl2 treatment suppressed the growth of a mouse fibroblast cell line (L cells) transfected with the wild-type ZF5 gene driven by the metallothionein promoter. Cells transfected with the wild-type ZF5 gene formed colonies two- to fivefold less efficiently than those transfected with the mutant ZF5 gene in P19, NIH3T3, 3T3-L1 and L cells. Over-expression of ZF5 did not cause c-myc down-regulation or arrest of the cell cycle, but increased the DNA content.

3T3 Cells↗