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K Oiwa

Publications and source records attributed to K Oiwa.

53 records · Page 3Linked to original sources
PubMed1989

Simultaneous recordings of force and sliding movement between a myosin-coated glass microneedle and actin cables in vitro.

To elucidate the molecular mechanism of muscle contraction resulting from the ATP-dependent actin-myosin interaction, we constructed an assay system with which both the force and the movement produced by the actin-myosin interaction in vitro can be simultaneously recorded and analyzed. The assay system consisted of the giant internodal cells of an alga, Nitellopsis obtusa, which contain well-organized arrays of actin filaments (actin cables) running along the cell long axis, and a glass microneedle (tip diameter, approximately 7 microns; elastic coefficient, approximately 40 pN/microns), which was coated with skeletal muscle myosin at the tip and extended from a micromanipulator at right angles with the actin cables. When the myosin-coated tip of the microneedle was brought into contact with the exposed surface of the actin cables, it exhibited ATP-dependent movement along the actin cables over a distance of 20-150 microns in 20-200 s (20-23 degrees C) and eventually stopped due to a balance between forces generated by the actin-myosin interaction (800-6000 pN) and by the bent microneedle. Since the load on the force-generating myosin molecules increased with the bending displacement of the microneedle (auxotonic condition), the relation between the load and the sliding velocity of the myosin heads past the actin cables was determined from the time course of the microneedle movement recorded with a video system. The shape of the force-velocity curve thus obtained was convex upwards, similar to that of the force-velocity curve of intact frog muscle fibers obtained under the auxotonic condition.

Actins↗
PubMed1989

Gene expression of terminal deoxynucleotidyl transferase in neoplastic cells of leukemia and lymphoma.

Expression levels of terminal deoxynucleotidyl transferase (TdT) mRNA in fresh leukemia and lymphoma cells were measured by northern blotting analysis. Bands of 2.1 kb mRNA were detected in all of eight cases of TdT activity-positive leukemias: two cases of null-cell acute lymphoblastic leukemia (null-ALL), two of common ALL, one of pre-B ALL, one of T-ALL, and two of chronic myelogenous leukemia in blastic crisis. One of the null-ALL and one of the common ALL cases also showed large TdT mRNA (3.3 kb). Since all TdT activity-positive samples exhibited TdT mRNA, the TdT gene might be mainly regulated at the transcription level in leukemic cells. An elevated level of 2.1 kb TdT mRNA was also detected in one lymphoma case, where neither TdT activity nor immunoreactive TdT was detected. The extensive chromosomal abnormality demonstrated in this case might be associated with the translational anomaly of TdT.

Blotting, Northern↗
PubMed1989

Effects of anti-interleukin-2 receptor antibody and cyclosporin A on human T cell proliferation in primary mixed lymphocyte reaction.

Effects of anti-IL2 receptor antibody (anti-IL2 RAb) and cyclosporin A (CsA) on human T cell proliferation in primary mixed lymphocyte reaction (MLR) were investigated. Both agents inhibited the proliferative response induced by alloantigen in a dose dependent manner when they were added at the initiation of culture. We also analyzed the expression of activation antigen on responder cells and the kinetics of T lymphocyte subset proliferation during MLR using two-color flow cytometry. Cells expressing activation antigens, such as IL-2 receptor and HLA-DR, were found less frequently in anti-IL2 RAb-treated MLR culture (4.8%) than in CsA-treated MLR culture (16.5%) on day 6. Furthermore, proliferation of CD8+CD11- cells, considered a cytotoxic T cell subset, were inhibited significantly more in anti-IL2 RAb-treated MLR culture than in CsA-treated MLR culture. We further demonstrate that CsA inhibits preferentially IL-2 production and anti-IL2 RAb inhibits T cell proliferation by blocking an absorption of IL-2 by activated lymphocytes. These data suggest that anti-IL2 RAb selectively inhibits alloantigen-activated T cells and may prove to be of significant value as an immunosuppressive agent in clinical organ transplantation.

Antibodies↗
PubMed1988

The force-velocity relationship for microtubule sliding in demembranated sperm flagella of the sea urchin.

We studied the relationship between the force and velocity of microtubule sliding in demembranated sperm flagella of the sea urchin, Hemicentrotus pulcherrimus, under auxotonic conditions following a quick release of the tension between sliding microtubules. The shape of the force-velocity curve was independent of the concentration of Mg-ATP over the range of 3.7 to 350 microM and appeared either linear or was the reverse of the hyperbolic curve seen for muscle. The power, calculated as the product of velocity and force, passed through a peak at c. 0.7 Fmax (the maximal isometric force). Thus, the maximal power is attained at a larger relative load than in muscle. The sliding velocity at 0.1 Fmax showed a hyperbolic dependence on Mg-ATP concentration, with a Km of 210 microM and a Vmax of 19 micron.sec-1. The maximal force did not significantly change over the Mg-ATP concentration range of 3.7 to 350 microM. These results are discussed in terms of a crossbridge model similar to the one originally proposed by Huxley. It is suggested that the dynein crossbridge cycle is characterized by a relatively rapid rate of attachment and a relatively slow rate of detachment.

Adenosine Triphosphate↗
PubMedDate not supplied

The structure of dynein-c by negative stain electron microscopy.

Dynein ATPases contain six concatenated AAA modules within the motor region of their heavy chains. Additional regions of sequence are required to form a functional ATPase, which a previous study suggested forms seven or eight subdomains arranged in either a ring or hollow sphere. A more recent homology model of the six AAA modules suggests that these form a ring. Therefore both the number and arrangement of subdomains remain uncertain. We show two-dimensional projection images of dynein-c in negative stain which reveal new details of its structure. Initial electron cryomicroscopy shows a similar overall morphology. The molecule consists of three domains: stem, head, and stalk. In the absence of nucleotide the head has seven lobes of density forming an asymmetric ring. An eighth lobe protrudes from one side of this heptameric ring and appears to join the elongated cargo-binding stem. The proximal stem is flexible, as is the stalk, suggesting that they act as compliant elements within the motor. A new analysis of pre- and post-power stroke conformations shows the combined effect of their flexibility on the spatial distribution of the microtubule-binding domain and therefore the potential range of power stroke sizes. We present and compare two alternative models of the structure of dynein.

Animals↗
PubMedDate not supplied

Enhanced thrombolysis induced by argatroban or activated protein C in the presence or absence of staphylokinase, measured in an in vivo animal model using mesenteric arterioles.

Successful administration of thrombolytic agents is associated with vessel reocclusion in a high proportion of cases. We have previously established an animal model to investigate platelet-rich thrombolytic mechanisms in vivo and demonstrated that recombinant staphylokinase (rSAK)-induced thrombolysis was enhanced by the concomitant administration of the direct thrombin inhibitor argatroban. The present study expanded the use of this model by comparing arterial and venous thrombolysis using advanced image analysis software. Mural thrombi were formed by Helium-Neon laser irradiation in mesenteric arterioles and were shown to be lysed, dose-dependently, by smaller amounts of rSAK than those required in venules. Activated protein C (APC), as well as argatroban, enhanced the rSAK-induced thrombolysis. APC or argatroban also induced thrombolysis in the absence of rSAK, and the effect was inhibited by tranexamic acid. The enhanced thrombolysis induced by APC or argatroban in the presence or absence of rSAK may be due to increased endogenous thrombolysis mediated by the inhibition of thrombin activity or delayed thrombin generation.

Animals↗