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Biomedical subjects

K Akazawa

Publications and source records attributed to K Akazawa.

At least 199 records · Page 11Linked to original sources
PubMed1982

Low molecular weight trypsin-plasmin inhibitors isolated from papain treated urinary trypsin inhibitor.

Papain treatment of human urinary trypsin inhibitor (UTI67; mol. wt. 43,000 by SDS-polyacrylamide gel electrophoresis, specific activity 1,897 U/mg protein) produced four new protease inhibitors, which were highly purified by gel chromatography on Sephadex G-100 and isoelectric focusing. The purified inhibitors (UTI26, UTI9-I, UTI9-II, and UTI9-III) were shown to be homogeneous by polyacrylamide disc gel electrophoresis, and had apparent molecular weights of 26,000, 9,000, 9,000, and 9,800, respectively, by sodium dodecyl sulfate gel electrophoresis. During enzymatic degradation of UTI67, the amino acid compositions changed to more basic, and the isoelectric point increased from pH 2.0 (UTI67) to pHs 4.4, 5.2, 6.6, and 8.3 (UTI26, UTI9-I, UTI9-II, UTI9-III), respectively. Both the parent and degraded inhibitors had anti-plasmin activity as well as antitrypsin and anti-chrymotrypsin activities. Much higher anti-plasmin/anti-trypsin and anti-plasmin/anti-chymotryspin activities were observed in the degraded inhibitors than in the parent UTI67. They competitively inhibited human plasmin with Ki values of 1.13 X 10(-7) - 2.12 X 10(-6) M (H-D-Val-Leu-Lys-pNA substrate). The reactions were very fast and the active site of the inhibitors of plasmin was thought to be different from that to trypsin or chymotrypsin.

Amino Acids↗
PubMed1982

Modulation of stretch reflexes during locomotion in the mesencephalic cat.

1. A cat preparation was used to study the modulation of stretch reflexes during locomotion. The brain stem was transected and locomotion was induced by electrical stimulation of the mesencephalic locomotor region below the level of transection. Three legs walked normally on a treadmill, while the fourth leg, which was denervated except for the soleus muscle, was held fixed. Brief length perturbations were applied to the soleus muscle at various phases of the stepping cycle.2. The stretch reflex in this muscle was deeply modulated during the step cycle, and reached its peak at or before the peak in soleus e.m.g. activity associated with the locomotion. A similar variation was observed when the sciatic nerve was stimulated electrically at a strength which elicited reflex activity (H wave), but did not directly elicit motor nerve activity (M wave). Variation in the reflex during electrical stimulation could not be accounted for by cyclic variation in fusimotor activity or in the afferent volley, but must be due to post-synaptic changes in alpha-motoneurones or in the presynaptic inputs to them.3. Large changes were also observed in intrinsic muscle stiffness during the step cycle. The maximum stiffness occurred near the time the limb would normally strike the ground during locomotion. A high stiffness would be useful in reducing the amount that the limb would yield under the weight of the body during the extension phase of the step cycle. The variation of the stretch reflex in parallel with stiffness suggests that reflexes could assist in this load compensation. The variation is not consistent with the idea that the stretch reflex is used to compensate for changes in intrinsic muscle properties, so that the total system behaves more like a spring of constant stiffness than does muscle alone.

Animals↗
PubMed1982

Immunochemical studies of high and low molecular forms of urokinase.

The immunochemical properties of high and low molecular forms of urokinase (HMW-UK, MW 53,000, 124,000 IU/mg protein; LMW-UK, MW 32,000, 230,000 IU/mg protein) were studied with specific antisera against the functionally active heavy chain (H chain, MW 31,000, 201,000 IU/mg protein) and the light chain (L chain, MW 18,000) of HMW-UK. Using a double immunodiffusion technique, LMW-UK did not demonstrate L chain antigenicity in the molecule. Anti-L-chain serum exerted no effect on LMW-UK and the H chain, but anti-H-chain serum strongly inhibited the fibrinolytic activity of all the active enzymes (HMW-UK, LMW-UK, and H chain). Anti-L chain serum was found to exert an antifibrinolytic effect on HMW-UK.

Animals↗
PubMed1982

Effect of urokinase on fibrinolysis and fibrinogenolysis.

The thrombolytic (fibrinolytic) effect of the urinary plasminogen activator, urokinase (UK), was compared with its fibrinogenolytic effect, using an artificial circulating system, and in in vivo pulmonary embolus and femoral vein thrombosis models. The thrombus lysing efficiency (fibrinolysis/fibrinogenolysis) was, in all cases, below 1.00, indicating that fibrinogenolysis is a primary function of UK while fibrinolysis is a secondary one.

Animals↗
PubMed1981

An electromyographic study of esotropia.

Under general anaesthesia the eye position of esotropia generally moved divergently. When retrobulbar anaesthesia was added bilaterally, the eye position moved further in the same direction. In the electromyogram under general anaesthesia the 4 horizontal recti were silent in controls. In many cases of esotropia, however, both medial recti showed a considerable amount of discharge under general anaesthesia. When retrobulbar anaesthesia was superimposed on one eye, the discharge from its medial rectus tapered off and, reciprocally, that of the opposite eye increased. These facts may suggest that proprioception plays in the development of esotropia.

Adolescent↗
PubMed1979

The number of active motor units and their firing rates in voluntary contraction of human brachialis muscle.

To make clear the control mechanism of force generation in human muscle, the electrical activity of the brachialis muscle was studied at various levels of contraction force by recording single motor unit discharges as well as mass electromyograms (EMGs). The firing rate of motor units increased with force along an S-shaped curve. At low levels of force, motor units increased their firing rates steeply with force. At intermediate levels of force, each motor unit increased its firing rate linearly with force at lower rates. As the maximum of force was approached, the firing rate increased very steeply, reaching as high as 50 Hz or more. By applying a new method of statistical processing to mass EMGs, the number of active motor units and the size of action potential were estimated at each level of force. The number of active motor units increased monotonously with muscle force. Motor units recruited at high levels of force had larger amplitudes of action potentials than those recruited at lower levels. Calculations were made to determine how the relative contribution to an increase in muscle force is varied between recruitment and the increase in firing rate. The contribution of recruitment gradually decreased with the increase in force. Up to about 70% of the maximum force, recruitment is the major mechanism for increasing the force of contraction.

Action Potentials↗
PubMed1976

A mechanochemical model for the steady and transient contractions of the skeletal muscle.

A mechanochemical model for muscle contraction was presented which consisted of three subsystems: the regulatory mechanism of contraction by Ca ion, the cross-bridge cycle coupled with actin-myosin interaction and the dynamics of contraction with an external load. It was assumed that both the rate constant of the cross-bridge cycle and the net force of the cross-bridge were linear functions of the sliding velocity. Most parameters in the model were determined from the experimental data, but several were estimated by simulation techniques. The model adequately described the force-load-velocity relation, the rates of energy and heat output as well as some basic mechanical properties of muscle. Not only the steady-state contraction but also the twitch response could be explained by the model. Time courses of tension and shortening during isometric and isotonic twitches were calculated by the model on a digital computer. The calculated curves agreed satisfactorily with the experimental ones obtained from the frog semitendinosus muscle. The rate of tension rise of the isometric twitch was shown to attain the peak at nearly the same time as does the calculated Ca concentration curve.

Actins↗