Search PubMed⌕ Search

Biomedical subjects

M Sokabe

Publications and source records attributed to M Sokabe.

At least 73 records · Page 4Linked to original sources
PubMed1990

The structure and dynamics of patch-clamped membranes: a study using differential interference contrast light microscopy.

We have developed techniques for micromanipulation under high power video microscopy. We have used these to study the structure and motion of patch-clamped membranes when driven by pressure steps. Patch-clamped membranes do not consist of just a membrane, but rather a plug of membrane-covered cytoplasm. There are organelles and vesicles within the cytoplasm in the pipette tip of both cell-attached and excised patches. The cytoplasm is capable of active contraction normal to the plane of the membrane. With suction applied before seal formation, vesicles may be swept from the cell surface by shear stress generated from the flow of saline over the cell surface. In this case, patch recordings are made from membrane that was not originally present under the tip. The vesicles may break, or fuse and break, to form the gigasealed patch. Patch membranes adhere strongly to the wall of the pipette so that at zero transmural pressure the membranes tend to be normal to the wall. With transmural pressure gradients, the membranes generally become spherical; the radius of curvature decreasing with increasing pressure. Some patches have nonuniform curvature demonstrating that forces normal to the membrane may be significant. Membranes often do not respond quickly to changes in pipette pressure, probably because viscoelastic cytoplasm reduces the rate of flow through the tip of the pipette. Inside-out patches may be peeled from the walls of the pipette, and even everted (with positive pressure), without losing the seal. This suggests that the gigaseal is a distributed property of the membrane-glass interface.

Animals↗
PubMed1990

Classification of the intrafusal muscle fibres in the frog muscle spindle: histochemical and immunofluorescent studies.

Intrafusal muscle fibres from bull-frog semitendinosus, iliofibularis and sartorius muscles were classified into three types using the histochemical, immunofluorescent and morphological characteristics, with reference to the extrafusal muscle fibres, which were classified into five types in accordance with Rowlerson & Spurway (1988). Immunofluorescent reactions with antibodies against slow or fast myosins obtained from anterior or posterior latissimus dorsi muscles (ALD or PLD), respectively, of chicken were used as the primary criterion. Histochemical profiles of muscle fibres were classified into nine types of myosin ATPase activity as the secondary criterion. Anti-PLD intrafusal fibres (polar zone) with ATPase profiles of moderate to high acid and alkaline stabilities correspond to large nuclear bag fibres in the classification of Diwan & Ito (1989), whereas anti-ALD fibres (polar zone) with alkaline-labile ATPase profiles correspond to medium nuclear bag fibres. On the basis of diameter, anti-PLD fibres (polar zone) with ATPase profiles of moderate to low acid stability and moderate to high alkaline stability seem to correspond to two types of small nuclear chain fibre. Variations between muscles, between intra- and extrafusal fibres and also between zones along intrafusal fibres are discussed.

Adenosine Triphosphatases↗
PubMed1989

Kanamycin induced low-frequency hearing loss in the budgerigar (Melopsittacus undulatus).

The chronic effects of kanamycin (KM) on hearing in the budgerigar were investigated by behavioral audiometry. The birds received a daily intramuscular injection of KM (100 mg/kg or 200 mg/kg) for 10 successive days, and absolute thresholds between pre- and post-treatment were compared. KM induced both transient and permanent low-frequency specific hearing loss; i.e., the elevation of threshold for frequencies below 1 kHz was greater than that for frequencies above 1 kHz. Moreover, the degree of hearing loss was dose dependent. The low-frequency selective effects of KM in the present study were contrary to the high-frequency specificity of aminoglycoside ototoxicity in mammals. To assess the effect of KM on auditory frequency resolution, critical ratios were estimated in pathological birds with low-frequency specific hearing loss. There was a linear relation between shift in critical ratio and shift in absolute threshold, suggesting that the increase in the critical ratio is due to a decrease in the efficiency of the detector mechanism rather than a change in the spectral resolving power of the birds.

Animals↗
PubMed1988

Modification of sensory-terminal responses and membrane structure of frog muscle spindle by collagenase.

A preparation of decapsulated muscle spindles with intact sensory innervation has been developed to allow direct access to the sensory terminal for the application of drugs or to alter the extracellular ionic composition. Muscle spindles were isolated from semitendinosus muscles of the frog Rana catesbeiana, and were incubated in a calcium-free Ringer's solution containing 0.2% collagenase. Following optimal incubation at 34 degrees C for 30 min the response pattern of the spindles during stretch could not be distinguished from that of intact spindles, although the duration of individual afferent spikes was prolonged about 4 times normal. The spikes disappeared immediately after the Ringer's solution was replaced with an isotonic choline chloride solution, in contrast to those of intact spindles which remained for 30 min after the replacement. Electron microscopy showed that the outer and inner capsules were partially disrupted. No significant change was observed in the size or packing density of intramembrane particles in freeze-fracture replicas of spindles decapsulated under optimum conditions. More prolonged treatment with the enzyme resulted in abolition of the static component of the response during stretch, and also in an aggregation of the particles, whose size decreased and packing density increased.

Afferent Pathways↗
PubMed1988

Effects of cyclic nucleotides and calcium on transduction and encoding processes in frog muscle spindle.

In decapsulated muscle spindles, application of dibutyryl cyclic AMP (d-cAMP, 0.1-10 mM) and forskolin (10-100 microM) increased the rate of spontaneous discharges and decreased the responsiveness to stretch. Addition of 2-5 mM CaCl2 or 0.5-2 mM BaCl2 to the above drugs prevented the deterioration of the responsiveness to stretch and the increase in the rate of spontaneous discharges. Similar changes in the afferent discharges were observed with application of isobutylmethyl-xanthine (IBMX, 0.5-2 mM) or carbonyl cyanide chlorophenylhydrazone (CCCP, 1-10 microM). Application of 0.1-1 mM quercetin resulted in a prolonged increase in the discharge rate, lasting 15-20 s after the release of stretch. These results suggest that cAMP is involved in the regulation of the sensory processes through a modification of intracellular calcium activity.

1-Methyl-3-isobutylxanthine↗
PubMed1988

Frequency specific susceptibility to acoustic trauma in the budgerigar (Melopsittacus undulatus).

The effects of intense noise exposure on hearing in the budgerigar were examined by behavioral audiometry. After binaural exposure to an intense broadband noise, auditory threshold shifts (TS) of the birds were continuously measured at frequencies between 0.125 and 8 kHz using an avoidance conditioning technique. Temporary threshold shifts (TTS) were observed at frequencies higher than 1.5 kHz and considerable permanent threshold shifts (PTS) were observed at frequencies below 1 kHz. This pattern of threshold shifts is contrary to that observed in mammals.

Acoustic Stimulation↗
PubMed1988

A cation channel for K+ and Ca2+ from Tetrahymena cilia in planar lipid bilayers.

The single-channel properties for monovalent and divalent cations of a voltage-independent cation channel from Tetrahymena cilia were studied in planar lipid bilayers. The single-channel conductance reached a maximum value as the K+ concentration was increased in symmetrical solutions of K+. The concentration dependence of the conductance was approximated to a simple saturation curve (a single-ion channel model) with an apparent Michaelis constant of 16.3 mM and a maximum conductance of 354 pS. Divalent cations (Ca2+, Ba2+, Sr2+, and Mg2+) also permeated this channel. The sequence of permeability determined by zero current potentials at high ionic concentrations was Ba2+ greater than or equal to K+ greater than or equal to Sr2+ greater than Mg2+ greater than Ca2+. Single-channel conductances for Ca2+ were nearly constant (13.9 pS-20.5 pS) in the concentrations between 0.5 mM and 50 mM Ca-gluconate. In the experiments with mixed solutions of K+ and Ca2+, a maximum conductance of Ca2+ (gamma Camax) and an apparent Michaelis constant of Ca2+ (K Cam) were obtained by assuming a simple competitive relation between the cations. Gamma Camax and K Cam were 14.0 pS and 0.160 mM, respectively. Single-channel conductances in mixed solutions were well-fitted to this competitive model supporting that this cation channel behaves as a single-ion channel. This channel had relatively high-affinity Ca2+-binding sites.

Animals↗
PubMed1987

Possible fusimotor innervation to frog muscle spindles.

In some muscle spindles located in or near the red area of semitendinosus muscle of the bull frog, a fine motor axon innervates the intracapsular compact zone, without any branches onto the extrafusal muscle fibers. The fine motor axon is 3.9 microns in mean diameter (measured in living axon) and 9.8 m X s-1 in mean conduction velocity at 20 degrees C. A ramp-and-hold stretch during 20 Hz repetitive stimulation of the fine motor axon markedly increased the rate of afferent discharges during static phase. Histochemical studies indicated depletion of glycogen in a compact zone along a small diameter intrafusal muscle fiber of the muscle spindles frozen immediately after tetanic stimulation of the fine motor axon. These results suggest that the fine motor axon is a fusimotor system in the frog muscle spindle.

Action Potentials↗
PubMed1987

Intramembrane particles and terminal responses following denervation of frog muscle spindles.

The sizes and population density of intramembrane particles in the non-myelinated sensory nerve terminals of frog muscle spindles were studied in comparison with changes in the responses to spindles to stretch 1-28 days after denervation. The sciatic nerve in the right leg was cut at the dorsal part of the hip joint. Spindle receptors in the left leg were used as controls. Muscle spindles were isolated from semitendinosus and iliofibularis muscles. The mean density of particles, which occurred mainly on the protoplasmic (P) face, declined rapidly to 60% of the control values 2 days after denervation, 30% after 4 days and to less than 10% after 7 days. The mean diameter of particles changed from 8.0 +/- 1.5 nm in the control to 12.8 +/- 2.5 nm 7 days after denervation. No significant difference between the results for the trunks (greater than 2 micron in diameter) and the branches (less than 0.5 micron) of the non-myelinated axons was observed. The peak rate of afferent discharges during a ramp-and-hold stretch survived up to 4 days after denervation, whereas the static component disappeared after 3 days. It is suggested that the decline to less than 20% of the control density of particles removes the mechanosensitivity of the sensory endings.

Animals↗
PubMed1987

An anion channel of sarcoplasmic reticulum incorporated into planar lipid bilayers: single-channel behavior and conductance properties.

An anion channel of sarcoplasmic reticulum vesicle has been incorporated into planar lipid bilayers by means of a fusion method and its basic properties were investigated. Analysis of fusion processes suggested that one SR vesicle contained approximately one anion channel. The conductance of this channel has several substates and shows a flickering behavior. The occupation probability of each substate was voltage dependent, which induced an inward rectification of macroscopic currents. Further, the anion channel was found to have the following properties. (1) The single-channel conductance is about 200 pS at 100 mM Cl-. (2) The channel does not select among monovalent anions but SO2-4 hardly permeates through the channel. (3) SO2-4 added to the cis side (the side to which SR vesicles were added) inhibits Cl- current competitively in a voltage-dependent manner. (4) An analysis of this voltage dependence suggests that the binding site of SO2-4 is located at about 36% of the way across the channel from the cis entrance.

Animals↗
PubMed1987

Detection of cyclic GMP binding protein and ion channel activity in frog rod outer segments.

In order to identify the cGMP-sensitive ion channel protein in frog rod outer segments (ROS), we analyzed cGMP binding proteins in the ROS by means of photoaffinity labeling with [3H]cGMP. We found four cGMP binding proteins with molecular weights (Mws) of 250K, 100K, 92K, and 53K. The 250K protein was an integral-membrane protein, which we named cG-Protein, (cG stands for cGMP). The cGMP-binding to cG-Protein was slightly increased by CaCl2. cG-Protein has a carbohydrate moiety. The amount of cG-Protein per single rod outer segment was estimated to be 9.0 x 10(6) molecules. Light-dependent phosphorylation of cG-Protein with [gamma-32P]ATP was observed. The 100K and 92K proteins were peripheral-membrane proteins, corresponding to cGMP phosphodiesterase. The 53K protein was a soluble protein. Incorporation of a membrane protein fraction of frog ROS into a planar lipid bilayer resulted in the appearance of at least three kinds of ion channel activities; two of them were related to cGMP. The possibility that cG-Protein is the cGMP-sensitive ion channel in vivo is discussed.

Animals↗
PubMed1986

Voltage-dependent aminoglycoside blockade of the sarcoplasmic reticulum K+ channel.

Single-channel conductance of the K+ channel from sarcoplasmic reticulum (SR) was reduced by aminoglycoside antibiotics such as neomycin and ribostamycin and also by n-hexylamine from either side of the membrane in a dose- and voltage-dependent manner. K+ channels were incorporated into an artificial phospholipid bilayer. This inhibition follows a single-site titration curve. The voltage dependence of the inhibition is explained by assuming that these drugs bind to the open state of a single channel on one site located approximately 40% of the way through the membrane from the cis side (the side to which SR vesicles are added) when drugs are added to the cis side and bind on another site located approximately 40% of the way through the membrane from the trans side (the opposite side to the cis side) when drugs are added to the trans side.

Amines↗
PubMed1985

Cation channels from Tetrahymena cilia incorporated into planar lipid bilayers.

A single cation channel from Tetrahymena cilia was incorporated into planar lipid bilayers. This channel selected for K+, Na+, and Li+ over Cl- and gluconate-, and its single channel conductance (at +25 mV) was 211 +/- 8 pS (mean +/- SE) in 100 mM K+-gluconate. The channel was not voltage dependent and may contribute to the resting K+ conductance of ciliary membrane.

Animals↗
PubMed1979

The application of the Gierer-Meinhardt equations to the development of the retinotectal projection.

Model calculations are presented for the several properties of the development of the retinotectal projection in amphibians and fishes, using the Gierer-Meinhardt equations. One of these properties is the maintenance of topographic mapping between the retina and the tectum during their development despite the fact that the two tissues grow in morphologically different ways. Another is the existence of a "critical period", at which the coordinates of the retina with respect to the tectum are irrevocably determined. It is assumed that the connections between the retinal and the tectal cells are made on the correspondence of positional markers which are given as a form of the distribution of a specific activator, the dynamics of which is described by the Gierer-Meinhardt equations. The monotonic distributions of the activator and the existence of the critical period are shown by a computer simulation of the proliferating retina. Several changes of the retinotectal projection after surgical operations on the retina or the tectum are also explained.

Amphibians↗
PubMed1979

Synergism and antagonism of neurons caused by an electrical synapse.

To investigate the role of electrical junction, a model system consisting of two electrically coupled neurons was studied. It was revealed that the model system generates both the in-phase pattern and the anti-phase pattern stably. Physiological condierations revealed the following. The in-phase discharge pattern (synergism) is a unique output of a electrically coupled pacemaker neurons. However, both the in-phase (synergism) and the anti-phase (antagonism) discharge patterns are possible for electrically coupled bursting neurons. We may expect other discharge patterns, such as a random discharge pattern (chaos), than the inphase and the anti-phase pattern in electrically coupled neurons. Random firing patterns in the inferior olive may be attributed to electrical synapses. Until now, we have assumed that excitation periods of two neurons were almost the same. When two periods are greatly different, various phenomena are expected. Determination of the stability of the anti-phase solution by the analytical methods, when diffusion constants are very small, is one of our future problems.

Action Potentials↗