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C Y Seow

Publications and source records attributed to C Y Seow.

43 records · Page 3Linked to original sources
PubMed1988

Velocity-length-time relations in canine tracheal smooth muscle.

Zero-load velocity (V0) as a function of the length of canine tracheal smooth muscle was obtained by applying zero-load clamps to isotonically contracting muscle under various loads. The load clamps were applied at a specific time after onset of contraction. The magnitude of the isotonic load therefore determines the length of the muscle at the moment of release or at the moment the unloaded shortening velocity was measured. A family of such V0-muscle length (L) curves was obtained at 1-s intervals in the time course of contraction. The V0-L curve was fitted by a parabolic function with satisfactory goodness of fit. The maximum shortening velocity at optimum muscle length varied with time, but the minimum length at which V0 diminished to zero was time independent.

Animals↗
PubMed1988

Fatigue of mouse diaphragm muscle in isometric and isotonic contractions.

Fatiguabilities of mouse diaphragm muscle in vitro in isometric and isotonic contractions were compared in this study. Isolated mouse diaphragm muscle was stimulated repetitively to induce fatigue during both isometric and isotonic contractions. The supramaximal electrical stimulation used was a train of 100-Hz, 0.5-ms pulses delivered to the muscle every 2 s for 0.5 s. The percentage decrease in isometric tension from beginning to end of the fatiguing process was used as the index of fatigue. The experiments were carried out at different PO2 levels in both normal and zero-glucose Ringer solutions. It was found that fatigue developed more rapidly in isotonic contractions than in isometric ones. Also, the extracellular glucose level demonstrated little effect on the muscle's short-term fatiguability, whereas reductions in the extracellular PO2 exerted a profound effect, especially in the case of isotonic fatigue.

Aerobiosis↗
PubMed1987

Time dependence of series elasticity in tracheal smooth muscle.

The stress-strain curve for the series elastic component (SEC) of tracheal smooth muscle was obtained by quick releasing the muscle from isometric tension to various afterloads and measuring the elastic recoils (SEC lengths) at a specific time after stimulation. A family of such curves was obtained by releasing the muscle at different points in time during contraction. Stiffnesses of the SEC (slopes of the stress-strain curves) at a specific stress level calculated from these curves (constant-stress stiffness) showed significant difference from one another. The same difference can also be characterized by the slope of the linear stiffness-stress curve, the constant A. The constant A during a 10-s isometric contraction was maximal at 2 s. It then decreased with time. This stiffness behavior is only seen when the effect of stress is held constant or eliminated. If stress is allowed to increase with time as it does during a tetanus then stiffness appears to increase monotonically. The SEC stiffness during active contraction was found to vary within the boundaries of the stiffness of muscle in rigor (upper limit) and that at resting state (lower limit).

Animals↗
PubMed1986

Force-velocity curves for smooth muscle: analysis of internal factors reducing velocity.

In tracheal smooth muscle, we obtained quantitatively different force-velocity (F-V) curves at early (2 s) and late (8 s) stages of an isometric tetanus whose contraction time was 12 s. These were essentially two samples from a continuum of F-V curves operating between 0 and 12 s. The cross-bridge cycling velocity at 8 s was slower and less sensitive to external load change compared with that at 2 s. This is possibly due to the presence of two types of cross bridges with different F-V characteristics; at 2 s most of the bridges resemble a cycling type, whereas at 8 s there is a population of what Dillon et al. have called slowly cycling or latch type interactions. Another possibility is that, due to some intrinsic factors, the whole population of cross bridges gradually change their F-V characteristics. Functions a(t) and b(t) were obtained by applying load clamps at 1-s intervals throughout a tetanus (a and b are asymptote values derived from the F-V hyperbolic curves): a increased with time, b remained constant. Analysis suggested that a/b was a valid index of internal factors that affect shortening velocity of unloaded muscle, and it is progressively increased in value during contraction.

Animals↗
PubMed1986

Changes in cross-bridge properties of sensitized airway smooth muscle.

We have reported previously that in ovalbumin-sensitized canine tracheal smooth muscle (TSM) the maximum ability to shorten is increased. This could account for the increased airway narrowing seen in vivo in allergic bronchoconstriction. It was associated with increased velocity of shortening. We now report that, by using an electromagnetic muscle lever system, quick releases were applied to control and sensitized TSM at 0.5-s intervals throughout the course of a lightly preloaded 10-s isotonic contraction. From the records obtained it is possible to determine that, early in contraction, shortening is brought about by relatively rapidly cycling [0.35 optimal muscle length units +/- 0.033/s (SE)] cross bridges. We also report that in the sensitized TSM it is the early bridges that increase their velocity by 26.6% (P less than 0.05) compared with similar bridges in muscles from control animals. Since 70% of the maximum shortening of the muscle occurs when early bridges are operative, it is likely that these bridges are responsible for the major part of the shortening. It is thus probable that increased allergic bronchoconstriction is produced by increased activity of early, rapidly cycling bridges. The bridges that are active late in the shortening show no difference between control and sensitized airway smooth muscles.

Animals↗