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Biomedical subjects

N Fujitsuka

Publications and source records attributed to N Fujitsuka.

At least 55 records · Page 3Linked to original sources
PubMed1992

Novel myosin isoform in nuclear chain fibers of rat muscle spindles produced in response to endurance swimming.

With the use of myosin adenosinetriphosphatase (ATPase) and immunofluorescence staining methods, the adaptive responses of intrafusal and extrafusal fibers to endurance swimming were studied in frozen sections of rat soleus (SOL) and extensor digitorum longus (EDL) muscles. Glycogen depletion confirmed muscle fatigue at the end of a standardized bout of exercise. No significant age-dependent changes in myosin isoforms were detected in any fibers. The 12-wk training increased type I fibers by 10.9% in the SOL and type IIa fibers in the EDL by 16.6%. In trained muscle sections, both staining methods identified a permuted chain fiber, expressed the same as the myosin isoform in the bag2 fiber. However, no exercise-induced change of myosin isoform profile was found in the bag1 and bag2 fibers. Myosin ATPase (and immunofluorescence) staining showed the percentage of permuted chain fibers increased from 0 to 6.7% (5.6%) after 6 wk of training and to 19.2% (14.1%) after 12 wk of training and that it was still at 6.1% (4.2%) 10 wks after training. A novel myosin isoform may thus be expressed in nuclear chain fibers by repetitive recruitment of muscle spindles.

Adenosine Triphosphatases↗
PubMed1991

Effects of ginsenoside-Rb2 on adenine nucleotide content of rat hepatic tissue.

In comparison with non-diabetic rats, the tissue ATP content of diabetic rats is lower and the AMP content higher. However, daily intraperitoneal administration of ginsenoside-Rb2 for several days resulted in an increase of tissue ATP content and a decrease of AMP content, characterized by an increase in the adenine nucleotide content, as well as improvement of energy charge. Thus, ginsenoside-Rb2 administration caused a change in the pattern of metabolism, activating the ATP supply system.

Adenine Nucleotides↗
PubMed1991

Production of methylguanidine from creatinine via creatol by active oxygen species: analyses of the catabolism in vitro.

The chemical oxidative conversion of creatinine (Cr) into methylguanidine (MG) has been followed by 1H-NMR and HPLC. By using active oxygen species generated by Fenton's reagent (Fe2+ and H2O2) or the similar reagent (Fe3+ and H2O2), creatol (CTL), a metabolite newly isolated from the urine of uremic patients, and creatones A and B were experimentally detected in the reaction mixture and implicated as successive intermediates in the pathway from CR to MG. An alternative oxidation of Cr to demethylcreatinine (glycocyamidine) was also observed. The importance of CTL in this in vitro oxidation mechanism is discussed.

Chromatography, High Pressure Liquid↗
PubMed1991

Studies on the precursor of methylguanidine in rats with renal failure.

Each of creatinine (Cr), guanidinoacetic acid (GAA) and arginine (Arg) was administered intraperitoneally to rats with renal failure, and the levels of methylguanidine (MG) in the serum, liver, kidney, muscle and urine were determined at certain intervals. The levels of MG in the serum, liver, kidney, muscle and urine after Cr administration increased markedly with time. The amount of total MG at 24 h was estimated to be 114 micrograms/100 g body weight, which accounted for 0.46% of the Cr dose. In contrast, changes in MG levels after administration of GAA or Arg were only slight in comparison with those after Cr administration. Thus, MG was proved to be produced mainly from Cr.

Animals↗
PubMed1990

Intramembrane particles and responses of sensory axon terminals during reinnervation of the frog muscle spindle.

Changes in the density of intramembrane particles (IMPs) of sensory nerve terminals in the bullfrog muscle spindle were correlated with recovery in the response of the spindle to stretch during postcrush reinnervation. A few IMPs on the protoplasmic (P) face in summer experiments (June to October) reappeared by the 3rd week after the nerve crush, then rapidly increased to 110% and 120% of control values 2 and 2.5 months after the crush. Afferent responses to stretch could be recorded after the mean IMP density on the P-face in terminal branches had recovered to more than 25% of the control value. The discharge rate showed a plateau pattern during the period of the excessive IMPs. This was supplanted by a normal pattern after a myelinated branch of the sensory axon was cut. The IMPs in winter experiments (November to April) reappeared by day 90 after nerve crush, and then slowly increased. The sustained responses to stretch reappeared after 5 months, when the mean IMP density on the P-face was restored to 25% or more of the control. Neither excessive density of the IMPs nor plateau pattern of the discharge rate were observed in winter experiments. The relation between the regenerated IMP densities and the functional recovery is discussed.

Action Potentials↗
PubMed1990

Production of methylguanidine from creatinine in normal rats and rats with renal failure.

Creatinine (Cr) was administered intraperitoneally to both normal rats and those given adenine, and time-course changes in methylguanidine (MG) production from Cr were compared. In rats with renal failure, the accumulation of MG in the body increased gradually with time after Cr administration. In particular, the MG level in skeletal muscle was markedly high in comparison with that in serum, liver or kidney, and a high concentration of MG was still present 24 h after Cr loading. In contrast, the amount of MG excreted into urine in these rats during 24 h after Cr administration was lower than the corresponding values in normal rats. Thus, the amount of MG per rat, distributed at 24 h after intraperitoneal administration of Cr 300 mg/100 g body weight was calculated. The production of MG from Cr was found to be markedly higher in rats with adenine-induced renal failure (172.09 micrograms/100 g body weight) than in normal rats (70.30 micrograms/100 g body weight). Produced MG was mostly excreted into urine in normal rats, whereas in rats with renal failure as much as 79.1% of produced MG was accumulated in the body.

Adenine↗
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

Creatine phosphate in fiber types of skeletal muscle before and after exhaustive exercise.

Percutaneous muscle biopsies were obtained from the vastus lateralis of physically active men (n = 12) 1) at rest, 2) immediately after an exercise bout consisting of 30 maximal voluntary knee extensions of constant angular velocity (3.14 rad/s), and 3) 60 s after termination of exercise. Creatine phosphate (CP) content was analyzed in pools of freeze-dried fast-twitch (FT) and slow-twitch (ST) muscle fiber fragments, and ATP, CP, creatine, and lactate content were assayed in mixed pools of FT and ST fibers. CP content at rest was 82.7 +/- 11.2 and 73.1 +/- 9.5 (SD) mmol/kg dry wt in FT and ST fibers (P less than 0.05). After exercise the corresponding values were 25.4 +/- 19.8 and 29.7 +/- 14.4 mmol/kg dry wt. After 60 s of recovery CP increased (P less than 0.01) to 41.3 +/- 12.6 and 49.6 +/- 11.7 mmol/kg dry wt in FT and ST fibers, respectively. CP content after recovery, relative to initial level, was higher in ST compared with FT fibers (P less than 0.05). ATP content decreased (P less than 0.05) and lactate content rose to 67.4 +/- 28.3 mmol/kg dry wt (P less than 0.001) in response to exercise. It is concluded that basal CP content is higher in FT fibers than in ST fibers. CP content also appears to be higher in ST fibers after a 60-s recovery period after maximal short-term exercise. These data are consistent with the different metabolic profiles of FT and ST fibers.

Adult↗
PubMed1989

Variations in the distribution of methylguanidine with the progression of renal failure after methylguanidine loading.

Methylguanidine (MG) was intraperitoneally administered to both normal rats and those given adenine, and MG levels in the serum, liver, kidney, muscle, brain and urine were compared. The accumulation of MG in the body increased with the progression of renal failure, whereas the rate of urinary excretion of MG in rats given adenine for 30 days was lower than the corresponding values in rats given adenine for 10 and 20 days. The velocity of MG elimination from serum and tissues became lower as the period of adenine administration lengthened. In particular, the rate of MG elimination from muscle was markedly low in comparison with that from the serum, liver, kidney or brain, and a high concentration of MG was still present 24 h after MG loading. In addition, the amount of MG obtained by subtracting the total amounts detected in the serum, liver, kidney, muscle, brain and urine from the dose decreased gradually as the period of adenine administration lengthened. The MG-scavenging effect is diminished according to the progress of renal failure.

Adenine↗
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↗
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

Fatigue during stretch-shortening cycle exercises. II. Changes in neuromuscular activation patterns of human skeletal muscle.

Detailed electromyographic (EMG) analysis of primarily triceps brachii muscle was carried out on subjects who performed 100 repeated and exhaustive stretch-shortening cycle (SSC) exercises on a special sledge apparatus incorporating a force plate. The fatigue contractions were performed on submaximal levels but the before-after comparison included also maximal "drop jumps" on the sledge as well as falls on to the floor. SSC contractions caused clear reduction in the mechanical performance capacity of the muscles. EMG analysis revealed that integrated EMG (IEMG) increased during the course of fatigue both during eccentric and concentric phases of the cycle. However, when IEMG was time-normalized, the changes were nonsignificant. The IEMG/force ratio increased especially during the eccentric phase both in submaximal and maximal drops. In maximal drops, there was also a great reduction in concentric IEMG. Rectified EMG curves were also averaged in blocks of ten successive fatigue contractions. This analysis revealed clear appearance of short (SLC), medium (MLC), and long (LLC) latency reflex components in most of the subjects during the early contact on the platform. The fatigue effects on these components were individual and also condition dependent so that in maximal drops there was a trend for reflex potentiation. In maximal drops on to the floor, which represented the highest stretch loads on the muscles, there was a tendency for reduction of amplitudes of the reflex components. The results suggest that in exhaustive SSC exercise muscular activation processes are reduced and primarily in the eccentric phase. Muscle spindles are suggested to become differentially affected by fatigue substances depending on the load intensity during eccentric contraction.

Biomechanical Phenomena↗