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T Tameyasu

Publications and source records attributed to T Tameyasu.

At least 19 recordsLinked to original sources
PubMed2004

Characterization of junctional sarcoplasmic reticulum Ca2+ content and release by short-term mechanical restitution in cardiac muscle.

To study Ca2+ handling by the junctional sarcoplasmic reticulum (JSR), the time course of short-term mechanical restitution after varying magnitudes of twitch contractions was assessed in rat papillary muscle. Mechanical restitution consisted of a pretwitch latency period followed by a rapid and a subsequent much slower restitution of twitch force. The rate of rapid restitution was independent of the magnitude of the preceding twitch, which suggests that the rate of JSR Ca2+ repletion was dependent on the amount of Ca2+ remaining in the JSR after a twitch contraction. Based on this finding, the functions Gt and Ht, representing the time courses of JSR Ca2+ repletion and release, respectively, were derived graphically from a family of the mechanical restitution curves. Gt increased monotonically with time at a decreasing rate, while Ht increased with time in a sigmoid manner. The mechanical alternans were simulated by using experimental values and mathematically predicted values of Gt and Ht. A substitution of extracellular Na+ with Li+ to inhibit Na+/Ca2+ exchange resulted in an augmentation of Gt by approximately 10%, presumably by increasing the tubular SR Ca2+ uptake. The inhibition of tubular SR Ca2+ uptake by thapsigargin (10 microM) reduced mechanical restitution by approximately 13% of the maximal twitch force, independent of the phase of mechanical restitution; the effect was greater at an earlier time point in the mechanical restitution. These results suggest that early JSR Ca2+ replenishment results mainly from the movement of Ca2+ from the tubular SR.

Adaptation, Physiological↗
PubMed2001

Effect of extracellular [Ca(2+)] on Ca(2+) release from sarcoplasmic reticulum in rat ventricular myocytes.

The effect of external [Ca(2+)] ([Ca(2+)](o)) on Ca(2+) release from the sarcoplasmic reticulum (SR) was examined with rested-state twitches in rat ventricular myocytes. The magnitude of transient rise of intracellular [Ca(2+)] ([Ca(2+)](i)) relative to the resting one, F/F(o), as measured with fluo-3, was 1.75+/-0.07 (mean+/-SEM, n=9) and 1.86+/-0.13 (n=9) at 0.3 and 1.8 mM [Ca(2+)](o), respectively; the difference was insignificant. The time from onset to peak and the rate of rise of the [Ca(2+)](i) transient were 0.107+/-0.017 s (n=9) and 18.8+/-3.38 F/F(o)/s, respectively, at 0.3 mM [Ca(2+)](o), they were 0.064+/-0.005 s (n=9) and 31.1+/-0.03 F/F(o)/s, respectively, at 1.8 mM [Ca(2+)](o). The difference in the corresponding values at the two [Ca(2+)](o) was significant (t-test, p<0.05). The half decay time of the [Ca(2+)](i) transient was 0.217+/-0.016 s (n=8) at 0.3 mM [Ca(2+)](o) and was similar to the value of 0.230+/-0.022 s (n=8) at 1.8 mM [Ca(2+)](o), indicating that the rate of decrease of [Ca(2+)](i) is independent of the [Ca(2+)](o). The duration of action potential was similar at 0.3 and 1.8 mM [Ca(2+)](o) as examined with papillary muscle. The results suggest that a lowering of [Ca(2+)](o), i.e., reducing the Ca(2+) influx, slows the rate of Ca(2+) release from the SR fully loaded with Ca(2+) with little effect on the total amount of the Ca(2+) release. An instantaneous relationship between the [Ca(2+)](i) and the myocyte shortening at 0.3 and 1.8 mM [Ca(2+)](o) suggested that the time course of unloaded contraction is related not only to the magnitude, but also to the rate of rise of [Ca(2+)](i).

Animals↗
PubMed2001

Intracellular [Ca(2+)] transients in Ca(2+) wave in single rat ventricular myocyte.

Ca(2+) release from the sarcoplasmic reticulum (SR) in heart muscle grades depending on Ca(2+) influx in the physiological twitch; Ca(2+( wave results from regenerative Ca(2+) release from the SR. To examine if the Ca(2+) release from the SR in the Ca(2+) wave takes a duration similar to the physiological one, a transient rise of intracellular [Ca(2+)] ([Ca(2+)](i) transient) was recorded during both a propagating Ca(2+) wave and an electrically evoked twitch with single rat ventricular myocytes, using a laser scanning confocal microscope. Care was taken to record the fluo-3 fluorescence from a segmental region with little lateral movement, especially during a propagating Ca(2+) wave. During a typical Ca(2+) wave, the time-to-peak (TP) and the half-width (HD) of the averaged [Ca(2+)](i) transient were 161 and 253 ms respectively, but they were 76 and 145 ms during an electrically evoked twitch. The difference in the duration between the two types of [Ca(2+)](i) transients could not be accounted for by modification of duration of [Ca(2+)](i) transient by possible asynchronous Ca(2+) release from the SR during a Ca(2+) wave, suggesting that the regenerative Ca2+) release from the SR in the Ca2+) wave occurs more slowly than the physiological one in rat ventricular myocytes.

Animals↗
PubMed1998

Implications of quantal motor action in biological systems.

We demonstrate in this paper that quantal behavior is a central feature of biological motile and contractile systems. Step-like behavior has been demonstrated in the interaction between single molecules and filaments both in the kinesin-microtubule system and in the myosin-actin filament system. We show here that the step-like molecular features appear also in the single intact sarcomere. We studied single sarcomeres of single bumble-bee myofibrils, both in the unactivated and activated states. Myofibril-length changes induced by a motor-imposed ramp were accompanied by corresponding sarcomere-length changes. However, the sarcomere-length changes were stepwise. Computer analysis of the stepwise shortening patterns revealed a step-size distribution containing multiple peaks. In the activated state, the peaks were separated by 2.7 nm per half-sarcomere which is the linear actin-subunit spacing. Thus, translation steps are an integer multiple of the actin-subunit spacing. This result parallels the one observed in the kinesin-tubulin spacing, where step size is a multiple of the tubulin-subunit spacing. In the muscle system, however, the steps are preserved on a macroscopic scale, implying high synchrony. The quantal steps are easily explained by a model in which the actin filament propels itself over stationary cross-bridges: if actin binds to the cross-bridges between steps, then the observed quantal result is inevitable. As probes of contractile phenomena approach the molecular level, the discrete unitary events underlying contraction begin to emerge. Thus, step-like behavior is observed as the single kinesin molecule translates along the microtubule, as the single myosin molecule translates over the actin filament, and as the single isolated titin molecule is stretched.

Actins↗
PubMed1998

Stepwise dynamics of connecting filaments measured in single myofibrillar sarcomeres.

Single relaxed myofibrils of bumblebee flight muscle were subjected to motor-imposed ramp-length changes. The image of the striations was projected onto a linear photodiode array, and sarcomere length was computed as the spacing between centroids of contiguous A-bands. Centroid position was determined by integrating the respective A-band intensity peak and computing the location at which the area on one side was equal to the other. The resulting trace of centroid to centroid span versus time was stepwise, with periods of rapid shortening alternating with periods of pause. An alternative nondiscrete sensor gave similar steps. If thick filament length remains constant, stepwise sarcomere length changes imply that length changes in the connecting filament must be stepwise. Thus, shortening of the connecting filament occurs as a sequence of discrete events rather than as a continuous event.

Animals↗
PubMed1998

Force-velocity relation of sliding of skeletal muscle myosin, arranged on a paramyosin filament, on actin cables.

To investigate in vitro ATP-dependent sliding of regularly arranged myosin molecules on actin filaments, we prepared thick hybrid filaments in which myosin molecules isolated from rabbit skeletal muscle were arranged around the paramyosin core (length, 10-20 micron; diameter, </=0.2 micron) obtained from a molluscan smooth muscle. A single to a few thick hybrid filaments were attached to a polystyrene bead (diameter, 4.5 micron; specific gravity, 1.5) and made to slide on actin filament arrays (actin cables) in the internodal cell of an alga, mounted on the rotor of a centrifuge microscope. The bead was subjected to centrifugal forces serving as external loads to the ATP-dependent actin-myosin sliding. The maximum unloaded sliding velocity of the thick filament attached-bead (mean, 3.4 micron/s; 20-23 degrees C) was significantly higher than that of the bead coated with randomly oriented myosin molecules reported previously. The steady-state force-velocity (P-V) relations obtained were qualitatively similar to those in intact skeletal muscle fibers. These results indicate that this in vitro motility assay system retains the basic characteristics of contracting skeletal muscle fibers, and that it may be effectively used to study mechanisms underlying the steady-state P-V characteristics of ATP-dependent actin-myosin sliding using various recombinant myosins produced in nonmuscle cells.

Actin Cytoskeleton↗
PubMed1998

Regulation of contraction in heart muscle. A Ca2+ gradient model for the Ca(2+)-induced Ca(2+)-release of the sarcoplasmic reticulum.

The sarcoplasmic reticulum (SR) in heart muscle releases a large amount of Ca2+ in response to a small amount of trigger Ca2+ by the mechanism of the Ca(2+)-induced Ca(2+)-release. A model was presented for the regulation of the SR Ca2+ release based on the assumptions that a Ca2+ gradient is formed from the level of Z-line toward the center of the cytoplasm as a result of continuous release of Ca2+ from the SR and that the volume of SR is quite small compared with the cytoplasmic volume. Numerical simulations showed that the amount of the SR Ca2+ release was dependent both on the initial SR Ca2+ content and the transsarcolemmal Ca2+ current. This interprets the effects of beat frequency and external [Ca2+] on twitch contractions in intact heart muscle. The present Ca2+ gradient model predicted that the reduction of the transsarcolemmal Ca2+ current alters the relation between the rate of rise and the peak of the cytoplasmic [Ca2+] in a twitch in such a way that lower the Ca2+ current, smaller the rate of rise of the cytoplasmic [Ca2+] at a given level of the peak cytoplasmic [Ca2+]. Measurements of the relations between the rate of rise and the peak of twitch force in rat papillary muscles and between the rate of rise and the peak of cytoplasmic [Ca2+] examined using fluo-3 in rat single heart myocytes were compatible with the prediction of the present model. Thus the model interpreted some important features in the regulation of the heart muscle contraction.

Animals↗
PubMed1996

Effect of a brief stretch on time course of shortening after a quick release in guinea pig tenea coli.

To examine the origin of velocity deceleration in the shortening of smooth muscle, guinea pig tenea coli which contracts isometrically in a high-potassium solution was released quickly (1st release), restretched to the original length, kept at this length for 0.06-0.2s and quickly released again (2nd release). The muscle shortened isotonically under the same very-light load after the 1st and 2nd releases. The length change of the muscle during shortening was examined using a video camera. The rapid shortening phase, seen after the 1st release, which followed the instantaneous, elastic recoil and lasted for about 0.3s, disappeared after the 2nd release. This effect was prominent when the stretch duration was short. The time course of the slow phase of shortening subsequent to the rapid one was not affected by stretching. These results suggest that the rapid shortening phase is due largely to adjust of the cross-bridges between the thick and thin filaments to the change from an isometric to an isotonic contraction, while the slow phase reflects a steady turnover in the cross-bridges. The velocity of the slow shortening phase reached a maximum before the isometric force peaked and decreased as the activation level was lowered by reducing the external Ca2+ concentration from 2.5 to 0.5 mM. This suggests that the steady turnover rate of the cross-bridges depends on the phase of contraction and level of activation. The cause of the gradual velocity decrease in the slow phase of shortening was discussed.

Animals↗
PubMed1994

Sarcomere dynamics in a spontaneous contraction wave and its effect on the following, electrically triggered twitch in rat myocyte. Comparison with the rested state twitch.

A spontaneous contraction (SC) wave propagates among sarcomeres in heart muscle by the mechanism of Ca(++)-induced release of Ca++ from sarcoplasmic reticulum (SR). In the present study, some characteristics of unloaded shortening during the SC and its effect on a subsequent, electrically triggered twitch (Tsc) were examined at a sarcomere level in isolated rat myocytes. The results were compared with those of a rested state twitch (RS), which was accompanied by an action potential. Average shortening velocity from onset to peak of shortening was 3.74 +/- 1.25 (mean +/- SD, n = 18) and 5.35 +/- 2.30 microns/s per sarcomere (n = 54) in SC and RS, respectively. That the former was smaller than the latter (P < 0.01, t test) suggests that Ca++ are released from the SR more slowly in the SC than the RS. There were no differences in either the extent or area of shortening between SC and RS. The extent of shortening increased significantly as shortening velocity increased in all the SC (P < 0.05), RS, Tsc, and triggered twitch (Trs) after the RS (P < 0.001 in the last three). The slope of the line for the regression of the extent upon the velocity of shortening in the SC was approximately 1.5 times greater than the other three. This suggests that the SC has a different time course of change of myoplasmic [Ca++] and therefore a different mode of the causal SR Ca++ release from the electrically triggered twitches (RS, Trs, Tsc). There were positive correlations between the extent and the area of shortening in each of the RS (P < 0.01), the Trs (P < 0.05), and the Tsc (P < 0.001), but not in SC. The slope of the line for the regression of the extent upon the area of shortening in the Tsc was about three times greater than those in the RS and the Trs, suggesting characteristics of the Tsc from different those of the RS and the Trs. An SC inhibited a Tsc in an interval-dependent manner. The shortening velocity in the Tsc recovered fully at a test interval of approximately 0.6 s between the onsets of the two successive contractions. The velocity increased further with further increasing the test interval (up to 0.9 s). At a test interval of 0.8-0.9 s, the shortening velocity in the Tsc was greater than those in the preceding SC and the corresponding Trs by 1.17- and 1.80-fold, respectively, as compared in the same five sarcomeres.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1994

Velocity and extent of electrically-triggered and spontaneous contractions in rat ventricular myocyte: relation to cell size and sarcomere length.

Characteristics of velocity and extent of unloaded contraction were examined at a cellular and a sarcomere level in isolated rat ventricular myocytes both during an electrically-triggered twitch and a contraction wave which occurred spontaneously at an end of the myocyte and propagated toward the other end. Both the velocity and extent of shortening examined at the cellular level in the triggered twitch were independent of the length and width of the myocyte. Among the myocytes isolated separately from the right ventricle and the inner and outer layers of the left ventricle, no differences were observed in any of their length and width, the velocity and extent of shortening. The extent of shortening examined at the sarcomere level was independent of the sarcomere length (SL) before the contraction in both the triggered twitch and the spontaneous contraction in the range of the SL examined (1.6-2.1 microns). The shortening velocity decreased as a decrease of the SL in the triggered twitch at both the cellular and sarcomere levels, while independent of the SL in the spontaneous contraction as examined at the sarcomere level. On the assumption that the shortening velocity reflects the rate of increase of myoplasmic free Ca2+ concentration ([Ca2+]in) and therefore the rate of Ca2+ release from the sarcoplasmic reticulum (SR), the above result suggests that the rate of the SR Ca2+ release is dependent on the SL before the activation in the electrically-triggered, action potential-mediated twitch, while independent of the SL in the spontaneous contraction without development of any action potential.

Animals↗
PubMed1994

Oscillatory contraction of single sarcomere in single myofibril of glycerinated, striated adductor muscle of scallop.

Unloaded contraction of a single sarcomere was studied on fiber fragments (1-micron thick, 4- to 6-microns wide, and less than 50 microns long) from glycerinated scallop striated muscle. The fragment was activated from rigor by a rapid solution exchange method. Sarcomere length (SL) was measured in the intensity profile caused by scanning the phase-contrast image of the striation of the fragment every 5.4 ms using an optical scanner-photomultiplier system with an accuracy of 0.04 micron. The sarcomere started to contract with a latency of 44 +/- 11 ms (mean +/- SD, n = 21) after the solution change. Averaging a few SLs in a fragment clearly revealed a phase, in which shortening was close to zero, preceded and followed by a rapid shortening phase. The contraction of a single sarcomere appeared to occur in an oscillatory manner with one or more of the zero-velocity phases during the observed period (up to 250 ms) when the data points were approximated with a polynominal curve. The distance between the near zero-velocity phases was 0.17 +/- 0.09 micron (n = 18). As the contraction was approximated with a staircase pattern consisting of a rapid shortening and a zero-velocity phase, the duration of the zero-velocity phase was 44 +/- 18 ms (n = 23). The velocity and the extent of the rapid shortening phase were 19.0 +/- 7.9 microns/sarcomere (n = 29) and 0.16 +/- 0.06 micron (20 degrees C), respectively, both of which were independent of the SL examined (1.7-2.6 microns). The velocity in the shortening phase was independent of the extent of the shortening but decreased with increasing duration of the shortening phase. Probably because of the loss of light chains relating to the Ca-regulation from some myosins during preparation, an increase in the concentration of ATP in the absence of Ca2+ resulted in a single shortening step of the sarcomere with a latency of 82 +/- 23 ms, followed by a phase of little shortening; the velocity in and the extent of the shortening step were 12.8 +/- 8.4 microns/s/sarcomere (n = 5) and 0.12 +/- 0.04 micron, respectively. The mechanism underlying the observed oscillatory contraction was considered in terms of the cross-bridge mechanism.

Animals↗
PubMed1992

Unloaded shortening after a quick release of a contracting, single fibre from crayfish slow muscle.

The time course of shortening at zero load was studied by the slack test method during tetanic contractions in isolated, single, slow muscle fibres of the crayfish. In 28 of 32 shortenings (from 14 different fibres) a biphasic shortening was seen, which consisted of an initial high-velocity phase lasting 3.3-20.8 ms and a following slow-velocity phase lasting for the entire time examined (up to 89.2 ms). Provided that the shortening occurred uniformly along the fibre length, velocity in the initial phase, V1, of the biphasic shortening was 14.4 +/- 3.4 (mean +/- SD, n = 10) microns s-1 per half sarcomere at Lo, the slack length, at 20 degrees C, while that in the second phase, V2, was 7.4 +/- 1.4 microns s-1 per half sarcomere. Lowering temperature decreased both V1 and V2 with Q10 = 1.4 for V1 and 2.0 for V2. Lowering the external Ca concentration from 15 mM, the standard, to 2 mM resulted in a tetanic tension below one-third of that at 15 mM Ca and decreased both V1 (t test; p < 0.01) and V2 (p < 0.001). Prestretching the fibre to 1.5 Lo had no significant effect on V2 (p < 0.3) but increased V1 (p < 0.001). The distance shortened during the initial high-velocity phase, LV1, was 4.0 +/- 1.8% Lo (mean +/- SD, n = 10) at 20 degrees C or about 0.14 microns per half sarcomere on average. LV1 was independent of the tetanic tension level when it was changed by lowering the external Ca concentration or temperature in the same fibre. Prestretching the fibre to 1.5 Lo, at which the sum of the active and the resting tension was lower than Po at Lo in two of three fibres, increased LV1 significantly (p < 0.001). The independency of LV1 from the tension level indicates that the initial high-velocity phase was not from shortening of some inert components in the fibre. One possibility is that the initial high-velocity phase was brought about by an acceleration of shortening by a compressive force, the origin of which has been discussed. The slow-velocity phase seemed to result from the crossbridge turnover with little exogeneous stress on myofilaments. Four different fibres exhibited an unloaded shortening with a constant velocity during the entire time examined (29.9-61.8 ms). This type of shortening had a velocity between the usual V1 and V2 values, suggesting that a compressive force accelerated the shortening during the entire time.

Animals↗
PubMed1991

Effects of calcium and ADP on tension responses to step length increases in glycerinated Mytilus smooth muscle.

To study the mechanical properties of various crossbridge states in the anterior byssus retractor muscle (ABRM) of Mytilus, the tension response of the glycerinated ABRM to a step increase of the length was examined in rigor solutions with saturating Ca2+ (Rca) and without added Ca2+ (R), rigor ones with ADP (AD) and with both ADP and saturating Ca2+ (ADca), and a low ATP, activating one. The application of ADca to a rigor ABRM caused a slow tension development of less than 0.083 kg/cm2 (n = 6) probably because of contaminant ATP in the presence of 0.25 mM p,p-di(adenosine-5')pentaphosphate (Ap5A) and 10 U/ml hexokinase with 2 mM glucose. The instantaneous stiffness in ADca was slightly smaller than that in the low ATP solution and greater than those in R, Rca, and AD, giving evidence that the stretch response reflected the mechanical property of the crossbridges. The rate of the tension decay during the initial 5 ms after the length change was completed was slowest in the ADca among the solutions examined, while during the initial 30-90 ms it was faster in the low ATP solution than R, Rca, AD, and ADca with little difference of the rate in the latter four solutions. The difference in the time course of the tension decay in between the low ATP solution and ADca may be taken to indicate that the high stiffness in ADca was not due to the formation of the tension-generating crossbridges but to the crossbridges with both bound Ca and ADP (AMCaADP) made directly from the rigor crossbridge (AM). Consequently, it was thought that AMCaADP was stiffer than AM and the crossbridges with either bound Ca (AMCa) or ADP (AM.ADP), the latter three kinds of the crossbridges being formed directly from AM, not as a result of ATP hydrolysis.

Adenosine Diphosphate↗
PubMed1990

Regulation of cross-bridge detachment by Ca ions at high ionic strength in molluscan catch muscle.

Changes in the profile of equatorial intensities of X-ray diffraction from an intact, anterior byssal retractor muscle (ABRM) of Mytilus were examined at rest, during contracture brought about by acetylcholine (ACh) and a subsequent rigor-like contraction caused by raising the tonicity of the external solution, and after returning the tonicity to normal. The results suggest that the cross-bridges formed between thick and thin actin filaments during the ACh-contracture were maintained in the hypertonic solution and broken on decreasing the tonicity before the recovery of spacing of the actin filament lattice. A similar rigor-like contraction was induced in glycerinated ABRM by increasing salt concentration during active contraction. The rigor-like force declined rapidly when Ca++ concentration decreased. The results suggest that the detachment of the cross-bridge from the actin filament is regulated by Ca++ at high ionic strength in the ABRM.

Acetylcholine↗
PubMed1989

Distribution of cross-bridges in isometrically contracting muscle: its deduction from the Huxley-Simmons theory and the effect of filament elasticity.

The author attempted to deduce a possible cross-bridge (XB) distribution as a function of x, the amount of stretch of the XB, by applying the Huxley-Simmons theory with their recent experimental data to a steady isometric contraction. I found no XB distribution which satisfied at once the Huxley-Simmons theory, their data and observations in muscle energetics and biochemistry. Further, a computation with a simple model suggested that the XB distribution could be broadened by the elasticity of the thick and/or the thin filament if it existed.

Elasticity↗
PubMed1985

Nonsteady motion in unloaded contractions of single frog cardiac cells.

We studied the mode of shortening of enzymatically isolated single frog cardiac cells with a high-speed videosystem to see whether or not shortening is smooth. The segmental shortening of the cell in response to electrical stimulation exhibited a clear pause following the initial shortening over a distance of approximately 11 nm/half-sarcomere. Several preparations showed a second pause following the initial one. Nonsteady motion with a pause lasted usually a few tens of milliseconds. The duration of nonsteady motion was shorter in cells with large velocities of steady shortening following the pause than those with smaller velocities.

Animals↗
PubMed1985

Force-velocity relation in paired frog sartorius muscles attached to opposite lever arms.

To study the mechanism of the longitudinal stability at the level of whole muscles, paired frog sartorius muscles were attached to the opposite lever arms at unequal distances from the pivot. The lever was initially fixed in position, and when the full isometric forces were developed in both muscles, it was released to move, the result being that the advantaged muscle shortened by stretching the disadvantaged one with a nearly constant velocity depending on the ratio between their points of attachment from the pivot. The force-velocity relation of the advantaged muscle was virtually identical with the ordinary force-velocity relation obtained from the isotonic release experiments, while the force-velocity relation of the disadvantaged muscle was found to be entirely different from the ordinary one because of a marked increase in the load-bearing ability. These results are discussed in connection with the enhancement of mechanical performance in lengthening muscle.

Animals↗