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Biomedical subjects

K Iwasa

Publications and source records attributed to K Iwasa.

At least 109 records · Page 6Linked to original sources
PubMed1988

Potassium Channels in Motor Cells of Samanea saman: A Patch-Clamp Study.

Leaflet movements in Samanea saman are driven by the shrinking and swelling of cells in opposing (extensor and flexor) regions of the motor organ (pulvinus). Changes in cell volume, in turn, depend upon large changes in motor cell content of K(+), Cl(-) and other ions. We performed patch-clamp experiments on extensor and flexor protoplasts, to determine whether their plasma membranes contain channels capable of carrying the large K(+) currents that flow during leaflet movement. Recordings in the "whole-cell" mode reveal depolarization-activated K(+) currents in extensor and flexor cells that increase slowly (t((1/2)) = ca. 2 seconds) and remain active for minutes. Recordings from excised patches reveal a single channel conductance of ca. 20 picosiemens in both cell types. The magnitude of the K(+) currents is adequate to account quantitatively for K(+) loss, previously measured in vivo during cell shrinkage. The K(+) channel blockers tetraethylammonium (5 millimolar) or quinine (1 millimolar) blocked channel opening and decreased light- and dark-promoted movements of excised leaflets. These results provide evidence for the role of potassium channels in leaflet movement.

Journal Article↗
PubMed1988

[An experimental study on preventive effect of vitamin E in spinal cord injury].

The effects of vitamin E on compression injury of the spinal cord associated with ischemia were studied in rats. Growing rats were divided into two groups and given diet containing 2 IU/100 g (group C) or 50 IU/100 g (group E) of alpha-tocopherol acetate from 8-10 weeks before experiments. The motor disturbance induced by spinal cord injury was greatly reduced by vitamin E-supplementation. After injury, the value of TBA-reactive substances (TBARS) was immediately increased and the level of alpha-tocopherol was correspondingly decreased in the spinal cord. A higher level of TBARS was observed in the proximal region than in the injured region of the spinal cord. The high level persisted for 24 hrs in group C, but decreased within 1 hr in group E. Pathological examination of the spinal cord revealed less damage, such as bleeding and edema, in group E than in group C.

Animals↗
PubMed1986

Evidence for interactions between batrachotoxin-modified channels in hybrid neuroblastoma cells.

Current records from voltage-clamped membrane patches containing two batrachotoxin-modified sodium channels were analyzed to determine whether these channels are identical and independent. In most two-channel patches, the experimentally observed probabilities that zero, one, or two channels are open differ from the binomial distribution, demonstrating that the two channels are nonidentical or nonindependent or both. From the same current records, we also determined the rate for the transition from two open channels to one open channel and for the transition from one open channel to zero open channels. These data are consistent with closing rates for the two channels that are equal and independent. Both probability and closing rate data can be fit by a model wherein the channels are identical, the closing rates are independent, and the opening rate is greater when the other channel is closed than when it is open. The implications of this model for analyzing noise spectra and current variance are examined.

Animals↗
PubMed1984

Ion channels in plasmalemma of wheat protoplasts.

The patch-clamp technique was used to study passive movements of ions through the plasmalemma of wheat leaf protoplasts. This method overcomes the problems inherent in conventional electrophysiological study of plant cells. Changes in conductance were recorded in patches excised from the plasmalemma. Two types of patches were observed: (i) regions of low channel density, where discrete single-channel currents could be resolved and conductance ranged from 10 to 200 picosiemens and (ii) regions of high channel density, where single-channel currents could not be resolved and conductance was on the order of a few nanosiemens. The results indicate a striking similarity between animal and plant cell membranes in the basic phenomena of transport. Moreover, the approach used constitutes a new degree of refinement in the study of processes of regulation, pathology, and toxicity in plants.

Calcium Chloride↗
PubMed1983

Co2+ and Mn2+ uptake by crab nerve fibers in resting state and potassium depolarization.

Transition metal ions, Mn2+ and Co2+, are incorporated into nerve fibers when they are applied externally. For nerve fibers in the resting state, however, extracellular and intracellular water may be distinguished by applying transition metal ions externally. NMR spectra of water protons from nerve fibers in high potassium media, which contain transition metal ions, consist of three or more components, reflecting a complex distribution of these ions around the nerve membranes. In the case of Co2+, three components may be identified.

Animals↗
PubMed1983

Osmotic properties of the squid giant axon and their modifications.

Volume and morphological changes of the squid giant axons in response to hyper- and hypoosmotic media were examined. In hyperosmotic media, which were made by adding sucrose or sodium chloride to the artificial seawater, the axons behaved approximately as ideal osmometers. The fraction of the osmotically inactive volume was less than 0.05. In hypoosmotic media down to half the osmolality of the artificial seawater, intact squid axons did not show significant volume increases. However, following a combined treatment with hyaluronidase and collagenase, the volume of the squid axons increased in these hypoosmotic media. A wrinkled pattern appeared on the surface of the axons while they were in hyperosmotic media containing excess NaCl or KCl. Trypsin treatment prevented appearance of this surface pattern. Furthermore, no such patterns appeared in media which were made hyperosmotic by the addition of sucrose or sodium glutamate.

Animals↗
PubMed1982

Further studies of rapid mechanical changes in squid giant axon associated with action potential production.

Mechanical changes in the squid giant axon associated with the production of an action potential are examined further by using piezoelectric and optical methods. The peak of swelling of the axon coincides with the peak of the action potential recorded internally at the site of mechanical recording. Mechanical changes produced by a train of action potentials do not summate. Repetitively fired action potentials induced by lowering the external Ca-ion concentration are preceded by a gradual swelling of the axon. An inward current through the membrane causes shrinkage and an outward current produced swelling of the axon. An inward current enhances and an outward current depresses the mechanical changes associated with the action potential. There is a transient shortening followed by an elongation of the axon when an action potential travels along the axon. It is argued that the experimental results obtained are consistent with the colloid chemical, or macromolecular, theory of excitation.

Action Potentials↗
PubMed1982

Rapid pressure changes and surface displacements in the squid giant axon associated with production of action potentials.

By using both optical and mechano-electric detectors, we have shown that the squid giant axon swells when an action potential is generated. The maximum swelling is reached at the peak of the action potential. The undershoot of the membrane potential is associated with a marked shrinkage of the axon. We have also demonstrated these mechanical changes in axons from which a major portion of the axoplasm has been removed. We have examined the effects of changing the tonicity of the external medium and of applying several chemical reagents.

Action Potentials↗
PubMed1982

Anion dependent swelling of crab nerve fibers during potassium- and veratridine depolarization.

Swelling of crab claw nerve fibers, monitored as weight increase, takes place while the nerve fibers are immersed in a medium high in K+, Cs+ or Rb+ concentration, or in artificial seawater to which 0.2 mM veratridine is added. Similar swelling is observed in nerves in sodium salt solutions which also contain low concentrations of divalent cations. The swelling observed under these conditions is dependent on anions, giving a series (from efficient anion to less efficient ones): I- greater than SCN- greater than Br- greater than Cl- much greater than F- greater than glutamate, ethylsulfate. The presence of this series indicates that the nerve swelling observed is attributed to influx of external salt. Uptake measurements of radioactive anions and cations corroborate the presence of salt influx under these conditions. In analyzing the anion dependence of nerve swelling, two factors, membrane and cytoskeletal structure, are examined. It is shown that the cytoskeletal structure, which is sensitive to the lyotropic series of anions, plays an important role in this phenomenon.

Animals↗
PubMed1981

Membrane-associated cytoskeletal proteins in squid giant axons.

Cytoskeletal proteins (e.g., tubulin, actin, and neurofilament proteins) in the squid giant axon are separable into KF-soluble and -insoluble forms. The KF-insoluble cytoskeletal components appear to constitute the major proteins in the subaxolemmal fibrous network on the inner surface of the axon. These cytoskeletal proteins and the subaxolemmal network are both highly soluble in KI solutions. Whereas giant axons tolerate prolonged perfusions in KF solutions with no loss of excitable properties, a relatively short perfusion with KI solution completely eliminates the excitability of the axon. The loss of this excitability correlates with the simultaneous dissolution of the subaxolemmal network of cytoskeletal proteins and the release of its proteins into the perfusate. These data support the hypothesis that cytoskeletal proteins associated with the inner surface of the axolemma are involved in the regulation of axonal excitability.

Animals↗
PubMed1981

Rapid mechanical changes in crab nerve and squid axon during action potentials.

1. By using a Fotonic sensor, it was found possible to record rapid mechanical responses of the crab nerve without a signal averager. 2. In squid giant axons, the peak of swelling was shown to coincide fairly accurately with the peak of the action potential. 3. Associated with propagation of an action potential along a squid giant axon, there is a small decrease followed by an increase in the length of the axon. 4. It was emphasized that both mechanical and birefringence responses of the squid axon are diphasic. 5. The origin of the mechanical responses in axons is discussed on the basis of the theories proposed by LOEB, HOBER and TEORELL.

Action Potentials↗
PubMed1980

Swelling of nerve fibers associated with action potentials.

Swelling of nerve fibers during the action potential was demonstrated by three different methods. Generation of a propagated nerve impulse in a crab nerve produced an outward movement of 50 to 100 angstroms of the nerve surfce and a rise in swelling pressure on the order of 5 dynes per square centimeter. In squid giant axons, the amplitude of the observed outward movement of the surface was small.

Action Potentials↗
PubMed1980

Mechanical changes in crab nerve fibers during action potentials.

A nerve impulse travelling along a crustacean nerve was found to be accompanied by a small, rapid movement of the nerve surface. The movement was 10-20 nm in amplitude and was concurrent with a rise in the "swelling pressure" of the order of 5 mg/cm2 for a nerve bundle. Initiation of an action potential at the site of cathodal polarization was preceded by a small, slow mechanical change in the nerve fiber. Anodal polarization produced a large mechanical change of the opposite sign. Tetrodotoxin and procaine suppressed rapid mechanical changes.

Action Potentials↗
PubMed1980

Swelling of nerve fibers during action potentials.

Nerve fibers swell concomitantly with the initiation of an action potential. Pronounced shrinkage follows the phase of swelling. These mechanical changes are attributed to the movement of water predicted by Teorell.

Action Potentials↗