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Biomedical subjects

E Miyazaki

Publications and source records attributed to E Miyazaki.

At least 145 records · Page 8Linked to original sources
PubMed1982

The differences in contractile response to AC field stimulation between longitudinal and circular muscles of guinea pig stomach.

Contractile response to AC field stimulation was compared between the longitudinal and circular muscles of the guinea pig stomach under various stimulating conditions. The longitudinal muscle responded with considerable tension at any frequency between 20 and 2,000 Hz. The circular muscle showed a peak response around 200 Hz with rapidly decreasing response to the higher frequencies of less than 800 Hz. Experiments in the presence of tetrodotoxin and atropine revealed that the circular muscle was scarcely stimulated directly (without nerve excitation) by the AC, while the longitudinal muscle was stimulated directly at frequencies higher than 400 Hz, as well as being stimulated indirectly at frequencies lower than 200 Hz. The field strength necessary to generate one-half maximum tension was higher in the circular muscle (2.8 V/cm) than in the longitudinal muscle (1.5 V/cm at 200 Hz), although when a frequency lower or higher than 200 Hz was applied, the strength-tension curve shifted to the left or right, respectively. The contractile responses of the two muscles were graded with respect to filed duration up to maximum tension. The maximum tension and the highest rate of tension development were given at the stimulating condition of 200 Hz, 5 V/cm, for 5 sec in both types of muscles. The maximum tension generated per unit cross-sectional area of the longitudinal muscle was 19.2 g/mm2 and that of the circular muscle was 32.5 g/mm2. The maximum rates of tension development of the longitudinal and circular muscles wer 9.1 and 12.1 g/(mm2 . sec), respectively.

Animals↗
PubMed1981

A comparison of the effects of temperature and metabolic inhibition on the contraction of smooth muscle.

The effects of temperature and metabolic inhibitors on short tetanus contraction of vas deferens were studied. The contraction height increased by lowering temperature from 35 degrees C, and decreased with a decrease in temperature below 25 degrees C. The maximum speed of contraction and relaxation decreased by lowering the temperature, showing a transition of Q10 values at 25 degrees C. The Q10 value for the maximum speed of contraction was 1.7 between 35 to 25 degrees C, and 5.3 between 25 to 10 degrees C. The Q10 value for the maximum speed of relaxation was 1.9 between 35 and 25 degrees C, and 13.0 between 25 and 15 degrees C. The time to peak tension and to half relaxation increased by lowering temperature. The Q10 values also showed a transition at 25 degrees C. The Q10 value for the time to peak tension was -2.5 between 35 and 25 degrees C, and -5.0 between 25 to 5 degrees C. The Q10 value for the time to half maximum relaxation was -3.1 between 35 and 25 degrees C, and -5.7 between 25 and 5 degrees C. NaN3 and KCN and DNP inhibited the contraction. However, time to peak tension and half maximum relaxation time were not altered. Although the maximum speed of contraction and relaxation decreased, this was caused only by the reduction in peak tension. O2-free or glucose-free treatment caused only a slight decrease in peak tension. Neither time to peak tension nor half maximum relaxation time was altered. The differences between the effects of temperature and metabolic inhibition are discussed.

2,4-Dinitrophenol↗
PubMed1980

Inhibitory action of lanthanum(La) on PGF2 alpha - induced contraction of guinea-pig stomach muscle.

The effects of lanthanum(La) on contractions induced by prostaglandin F2 alpha(PGF2 alpha) or isotonic K+ were investigated in the isolated stomach muscle of guinea-pig. Low concentrations of La( 0.1-1 microM) inhibited the contraction to PGF2 alpha 1 microM in a dose-dependent manner, without affecting the tonic contraction to isotonic K+. 0.1 and 1 microM La shifted the dose-response curve for PGF2 alpha( 0.001 - 1 microM) to the right and reduced the maximum response. The IC50 of La against PGF2 alpha and K+ were 0.6 microM and 30 microM, respectively. These results support the suggestion that PGF2 alpha -induced contraction in the stomach muscle depends mainly on the intracellular release of sequestered Ca, which would be depleted or immobilized by La.

Animals↗
PubMed1979

Structural analysis of functionally different smooth muscles.

The ultrastructure of the longitudinal and circular muscle cells of the guinea pig stomach which show different contractile responses was compared. The extracellular space within the muscle bundles is about 12.1% in the longitudinal layer and about 4.4% in the circular layer. Nexuses were sonsistently found in the circular muscle layer but not in the longitudinal muscle layer. Numbers of both mitochondria and microtubules per unit area of smooth muscle cell are larger in the longitudinal than in the circular muscle. Cellular area occupied by sarcoplasmic reticulum is about 4.7% in the longitudinal muscle, 2.3% in the circular muscle. The numbers of caveolae are almost the same in both tissues. The most distinct difference between the two types of smooth muscle is the appearance of the thick filaments. The circular muscle cell contains approximately 50 thick filaments per 0.5 micron 2 of cytoplasmic area, while the longitudinal muscle cell only about 25 filaments which were usually much thinner than those of the circular muscle. These results indicate that the contractile apparatus itself is different in longitudinal and circular smooth muscles of the guinea pig stomach.

Animals↗
PubMed1979

[Stimulating effects of alanine and glycine on guinea-pig taenia coli (author's transl)].

Effects of alanine and glycine on the mechanical and electrical activities of guinea-pig taenia coli were investigated. Alanine (0.1--10 mM) and glycine (0.5--10 mM) produced a dose dependent contraction of guinea-pig taenia coli. The stimulating effects of alanine and glycine were not inhibited in the presence of atropine (5 muM), tetrodotoxin (0.1 micrograms/ml), diphenhydramine (4 muM), methysergide (3 muM), strychnine (10 muM), and were not influenced by treatment with indomethacin (3 muM). However, these effects were inhibited in the presence of a Ca antagonist, verapamil (10 muM). When the electrical activities of the taenia coli were recorded by the single sucrose-gap method, alanine and glycine (5--10 mM) produced a reduction of membrane potential and increased spike heights and frequencies of action potential. In LiCl or Choline-Cl and in Na-isethionate solutions, the stimulating effect of alanine was not abolished, but was completely inhibited in KCl-depolarized preparation. From these results, it is considered that both alanine and glycine may directly produce contraction by a depolarization of the cell membrane of guinea-pig taenia coli.

Action Potentials↗
PubMed1978

Prostaglandin F2alpha (PGF2alpha)-induced contraction and calcium movement in longitudinal muscle of guinea-pig isolated stomach.

Calcium movement and contractile responses to high K+ concentration and PGF2alpha were investigated in guinea-pig stimach longitudinal muscle. High K+ concentration (30 mM) and PGF2alpha (10(-7) M) produced similar contractions of guinea-pig stomach longitudinal muscle. The 'Ca-antagonist', verapamil (10(-5)-10(-4) M), prevented high K-induced contraction, but did not greatly reduce contractions to PGF2alpha. 45Ca uptake was increased by high K(30 mM) or PGF2alpha(10(-7) M). These increases in 45Ca uptake were greatly reduced with 10(-4) M verapamil. The results suggest that high K-induced contraction may depend on an increase in Ca influx. PGF2alpha-induced contraction may depend on both an increase in Ca influx and on an intracellular release of Ca.

Animals↗
PubMed1977

Calcium and the contractile response to prostaglandin in the smooth muscle of guinea-pig stomach.

In the longitudinal smooth muscle of guinea-pig stomach, verapamil (10(-5) M) which showed marked suppression of high K-induced contractures, did not suppress the contractile response to PGE1 (1.5 X 10(-9) to 10(-6) M) markedly. These results suggest that the contractile mechanism of PGE1 in guinea-pig stomach may mainly depend on a release of bound Ca in the cell and partly depend on a Ca influx from the extracellular origin.

Acetylcholine↗
PubMed1976

Inhibitory actions of polyphloretin phosphate and related compounds on the response to prostaglandin in the smooth muscle of guinea-pig stomach.

The inhibitory actions of polyphloretin phosphate (PPP) and related compounds, di-4-phloretin phosphate (DPP), PHLORETIN AND TRIHYDROXY PROPIOPHENONE (THPP) on the contractile responses to prostaglandin (PG) and acetylcholine (ACh) in longitudinal smooth muscle of guinea-pig stomach were studied. Of the four inhibitors PPP and DPP showed relatively selective antagonism for PGE1. DPP gave the highest pW2 value against PGE1. These results indicate that DPP is a useful antagonist of PG in smooth muscle, although it slightly inhibits responses to ACh, 5-HT or histamine, and the Ca-induced contracture in K depolarized preparation.

Acetylcholine↗
PubMed1976

Ca binding of intestinal smooth muscle myosin B.

By means of both centrifugation and filtration techniques, the Ca binding activity of intestinal myosin B was studied. The binding capacity of myosin B was Ca dependent and was approximately linear when the concentration of Ca in the medium ranged from 10(-4) to 10(-7) M. The Ca sensitivity of ATPase activity in the same range of Ca concentration exhibited a sigmoid curve. The Scatchard plot of Ca binding showed that intestinal myosin B had at least two types of binding sites. One of these was defined as a high affinity site with an apparent affinity constant of 2.5 x 10(6) M-1. The other was supposed to be a low affinity site of Ca binding. Mild trypsin treatment reduced the Ca binding capacity of intestinal myosin B by 1.45-2.44 nmol/mg protein. These values are approximately the concentration of the high affinity Ca binding sites in the intestinal myosin B. A major concern regarding the effect of trypsin is that the reduction of Ca binding surely accompanied the elimination of Ca sensitivity of myosin B ATPase activity. From these results, it seems likely that the high affinity sites of Ca binding identified in this study are based on the troponin-like component included in intestinal myosin B.

Adenosine Triphosphatases↗
PubMed1975

Effect of prostaglandin F2 alpha on propulsive activity of the isolated segmental colon of the guinea-pig.

The effects of prostaglandin F2alpha (PGF 2alpha) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated. Using experimental conditions under which spontaneous propulsive activity was negligible, PGF2alpha (5X10(-8)X1X10(-6)M), added to the bathing medium increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1X10(-7)g/ml). The contractions produced by PGF2alpha (5X10(-7) -1X10(-5)M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1X10(-7) g/ml). From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF2alpha may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.

Animals↗