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M M Dewey

Publications and source records attributed to M M Dewey.

At least 19 recordsLinked to original sources
PubMed1994

Dynamic laser light scattering studies of the effects of pyrophosphate on cyclic motions of cross-bridges in isolated thick myofilaments from Limulus striated muscle.

Pyrophosphate (PPi) is a non-hydrolyzable ATP analogue known to affect the binding between myosin heads and actin. By using a dynamic laser light scattering method, we have shown that 1-2 mM PPi enhances the increase in gamma values induced by Ca2+ in isolated thick myofilaments from Limulus striated muscle. However, similar treatment has no effect on the gamma values of filaments suspended in either relaxing solution or ATP-free solution. gamma is the average linewidth of the photoelectron count autocorrelation function of the light scattered. PPi had no effect on the increase of gamma values by Sr2+ but it substantially increased the gamma values of the thick myofilaments suspended in Ba(2+)-substituted Ca2+ activating solution. The results show that PPi also affects the energy-requiring cyclic cross-bridge motions.

Actin Cytoskeleton↗
PubMed1992

Suppression of crossbridge motions of isolated thick myofilaments in ATP-free medium by thiourea.

Thiourea is known to suppress the contractile response of Mytilus anterior byssus retractor muscle and toad sartorious muscle following electrical or chemical stimulation without abolishing of the electrical responses. In addition, it blocks the shortening of glycerinated sartorious muscle induced by Ca2+. With dynamic laser light scattering method we found that thiourea suppresses the increase of the average linewidth of the photoelectron count autocorrelation function, gamma, of isolated thick filaments of Limulus striated muscle induced by depletion of ATP. The results obtained suggest that thiourea prevents the crossbridges from moving away from the thick myofilament backbones which will, in turn, prohibit the crossbridges from interacting with the thin myofilaments.

Adenosine Triphosphate↗
PubMed1992

Seasonal changes in the activation of crossbridge motions of isolated thick filament from Limulus striated muscle.

In dynamic light scattering, measurements of the intensity-intensity time correlation function from a suspension of rod-like particles of length L could reveal dynamical information related to translational and internal motions of those particles. For a suspension of thick filaments isolated from the myosin-regulated, striated muscles of Limulus at KL greater than 1 (where K is the scattering vector), the average characteristic linewidth (gamma) increased with the addition of Ca2+ or with the depletion of ATP. The increase in the gamma with the addition of Ca2+ could be due to the presence of energy-requiring, high-frequency motions of the crossbridges activated by Ca2+. The increase in gamma which occurred with the depletion of ATP was assumed to be mainly due to the thermal motions of the crossbridges after they had moved radially away from the filament backbone. The percentage increase in gamma following the addition of Ca2+ was found to be seasonal, i.e., values of gamma obtained from thick filaments isolated between the middle of June and the middle of September were smaller than those obtained during the rest of the year. The effect of temperature on the percentage increase in gamma was also different. The increase showed a maximum at about 35 degrees C during the summer and at about 25 degrees C at other times. However, the percentage increase in gamma developed under ATP-depleted conditions showed no temperature-related maximum. The number of bound Ca2+ per myosin molecule was 1 during the summer and 2 at other times.

Adenosine Triphosphate↗
PubMed1987

Effect of ATP depletion on the isolated thick filament of limulus striated muscle.

With the dynamic light scattering method, we have shown that calcium ions increase the high-frequency internal motions of isolated thick filaments of Limulus striated muscle in the presence of ATP (Kubota, K., B. Chu, Shih-fang Fan, M.M. Dewey, P. Brink, and D. Colflesh. J. Mol. Biol. 1983. 166:329 and Fan, S.-f., M.M. Dewey, D. Colflesh, B. Gaylinn, R. Greguski, and B. Chu. Biophys. J. 1985. 47:809). If ATP is removed from the suspending medium, an increase of high-frequency internal motions also has been observed with characteristics different from those of filaments suspended in a medium containing ATP and calcium ions. These internal motions appear whether calcium ions are present or not and are suppressed by trifluoperazine (TFP). The motions differ from the calcium ion-induced motions in that (a) an energy supply is not required; (b) they are insensitive to heat treatment (42 degrees C, 10 min) and (c) they are also insensitive to phenylmethylsulfonyl fluoride which blocks the motions in the presence of ATP and calcium ions (Fan, Shih-fang, M.M. Dewey, D. Colflesh, B. Gaylinn, R. Greguski, and B. Chu. 1985. Biochim. Biophys. Acta. 827:101). Electron micrographs of negatively stained thick filaments in an ATP-free medium show that the majority of crossbridges extend out from the backbone of the filament and optical diffraction patterns from these filaments lack layer lines arising from the crossbridges. The flexibility of the thick filaments suspended in ATP-free media increases.

Adenosine Triphosphate↗
PubMed1986

Paramyosin and myosin content of the thick filament in the striated muscle of Limulus.

The thick myofilaments of the striated muscle from the horseshoe crab (Limulus) are composed of the proteins paramyosin and myosin. Using quantitative gel electrophoresis we find that there are 1.02 paramyosin molecules for every myosin. This protein composition is consistent with scanning transmission electron microscopy measurements of isolated thick filament mass and the four-stranded helical filament structure reported previously by others if one assumes one myosin molecule per surface subunit as has been suggested. Polyclonal antibodies were used to distinguish myosin and paramyosin bands from others of similar electrophoretic mobility as well as to detect aggregates and breakdown products by examination of gel patterns transferred to nitrocellulose membranes. Two-dimensional gel maps were utilized as a check for coelectrophoresing bands that might go undetected in one dimension. Coomassie Blue binding per mg of purified myosin or paramyosin was found to differ by less than 5%. Extinction coefficients for Limulus myosin and paramyosin as calibrated to dry weight measurements are also reported.

Animals↗
PubMed1985

Suppression of active cross-bridge motions of isolated thick myofilaments in suspension by phenylmethylsulfonyl fluoride.

Studies of photoelectron count autocorrelation function of light scattered from suspensions of thick filaments of Limulus telson muscle and scallop striated adductor muscle reveal that Ca2+ can activate cross-bridge motions of these isolated filaments. By treating suspensions of activated filaments with phenylmethylsulfonyl fluoride (PMSF), we can suppress active cross-bridge motions but not affect the Ca2+-dependent ATPase activity.

Adenosine Triphosphatases↗
PubMed1985

The active cross-bridge motions of isolated thick filaments from myosin-regulated muscles detected by quasi-elastic light scattering.

Intensity fluctuation spectroscopy has been used successfully as a probe that can detect an increase in high-frequency internal motions of isolated thick filaments of Limulus muscle upon the addition of calcium ions. We have attributed such motions to cross-bridge motion instead of to an increase in the flexibility of the filament backbone. Here we show that after cleavage of the S-1 and then the S-2 moieties with papain, cross-linking the myosin heads to the filament backbone, or heat denaturation (42 degrees C, 10 min), the increase in the high frequency internal motions in the thick filaments no longer occurs. Congo Red, which has been shown to induce shortening of isolated myofibrils, also increases the high-frequency motions of the isolated filaments. Furthermore, the increase is suppressed by treating the filaments with a myosin ATPase inhibitor such as vanadate ions (10 mM) or by replacing ATP with either an equimolar CrADP or the nonhydrolyzable ATP analogue beta, gamma-imido-adenine-5'-triphosphate (AMP-PNP). Calcium ions have a similar effect on isolated thick filaments from scallop muscle, where the myosin is known to be regulatory. Calcium ions have no such effect on thick filaments isolated from frog muscle, which is believed not to be regulated by calcium binding to myosin. These results confirm our earlier supposition that the additional high frequency internal motions of the thick filaments isolated from striated muscle of Limulus are related to the energy dependent, active cross-bridge motions.

Adenosine Triphosphatases↗
PubMed1984

Limulus striated muscle provides an unusual model for muscle contraction.

Although nearly two decades have passed since de Villafranca (1961) described A-band shortening, controversy persists. Here we will review the data which has been amassed since de Villafranca 's description. We will conclude that A-bands and thick filaments shorten during sarcomere shortening in Limulus striated muscle. Further we will suggest that two machines operate in this muscle: a tension generating sliding filament system and a tension generating thick filament shortening system. Also we will suggest a mechanism of force generation of the filament shortening system and provide evidence for a cycling bridge mechanism for this muscle.

Animals↗
PubMed1984

Dynamic laser light scattering of papain-treated thick filaments from limulus striated muscle in suspension.

Using quasielastic light scattering we have previously shown an increase in high frequency internal motion of isolated thick filament upon activation. This we have attributed to cross-bridge motion. Here we show that after cleavage of the S1 moiety of myosin from isolated filaments with papain, calcium ions no longer activate the isolated filaments to produce high-frequency motions.

Animals↗
PubMed1983

Quasi-elastic light scattering of suspensions of Limulus thick myofilaments in relaxed (long) activated and rerelaxed (short) states.

Photoelectron count autocorrelation function of light scattered by Limulus thick myofilament suspensions was measured as a function of scattering angle in the relaxed, activated and rerelaxed states. By using the cumulants method of data analysis, the average linewidth over large ranges of KL (up to 120), has been calculated with K and L being, respectively, the magnitude of the momentum transfer vector and the length of the myofilament. We have observed a dramatic increase in the average linewidth denoting the presence of additional high frequency components for the myofilament suspension on the activated state. By confirming our results on the size of the myofilaments from electron micrographs, we are able to attribute the high frequency (kHz) components to the "correlated" cross-bridge motions, representing, to our knowledge, the first direct experimental evidence of such movements in isolated thick myofilament suspensions.

Animals↗
PubMed1980

Evidence for fixed charge in the nexus.

The nexus or gap junction has been characterized as a low-resistance junction as well as a highly permeable junctional membrane to many molecules. The transfer of electrical current from one cell interior to another, the aqueous solubility of dyes used to trace cell to cell communication and the fact that these molecules move across the nexus more rapidly than the plasma membrane have led to the hypothesis of an aqueous channel in the junction. Both Ca2+ (ref.11) and H+ (ref. 12) are thought to alter nexal membrane conductance, and a voltage-sensitive gate has been demonstrated within the junction. Recently, Flagg-Newton et al. have concluded that mammalian junctions may contain fixed charge or be of smaller diameter than arthropod junctions. Here we have investigated these alternatives by examining the permeability of nexuses of septa of the median giant axon of Lumbricus terrestris with various derivatives of fluorescein. Both carboxyfluorescein and aminofluorescein were found to have depressed permeabilities relative to their predicted permeabilities based on molecular size and weight (MW). Flourescein diffusion was significantly suppressed in axons pre-injected with aminofluorescein but carboxyfluorescein had no such effect (Table 1). These data suggest the existence of fixed anionic charge within the nexal channel which may have affinity for amino groups.

Action Potentials↗
PubMed1980

Length-tension relation in Limulus striated muscle.

Laser diffraction techniques coupled with simultaneous tension measurements were used to determine the length-tension relation in intact, small (0.5-mm thick, 10-mm wide, 20-25-mm long) bundles of a Limulus (horseshoe crab) striated muscle, the telson levator muscle. This muscle differs from the model vertebrate systems in that the thick filaments are not of a constant length, but shorten from 4.9 to approximately 2.0 micrometers as the sarcomeres shorten from 7 to 3 micrometers. In the Limulus muscle, the length-tension relation plateaued to an average maximum tension of 0.34 N/mm2 at a sarcomere length of 6.5 micrometers (Lo) to 8.0 micrometers. In the sarcomere length range from 3.8 to 12.5 micrometers, the muscle developed 50% or more of the maximum tension. When the sarcomere lengths are normalized (expressed as L/Lo) and the Limulus data are compared to those from frog muscle, it is apparent that Limulus muscle develops tension over a relatively greater range of sarcomere lengths.

Animals↗
PubMed1979

Action potentials can propagate along small strands of smooth muscle.

Bundles of taenia coli muscle as small as 25 micrometers in diameter were dissected from guinea pigs and incubated in an organ culture media for several days. We found that use of an organ-culture bathing solution greatly extended the in vitro responsiveness as well as survival of such small bundles. Electronmicrographs showed that surviving strands of cells constituted only a very small fraction of the cross section of these bundles. Nonetheless, still they supported propagating nondecrementing action potentials. This means that in some cases strands, only a few cells in cross section, supported propagating action potentials. The long length constant and parallel orientation of cells provide a basis assuming cells act as parallel core conductor segments. For these reasons we have called into question the notion that for propagation to occur there must be a facilitating cooperation between large numbers of smooth muscle cells in parallel. Indeed we suggest that the limiting size for propagation is a strand of single cells.

Action Potentials↗
PubMed1979

The effect of lanthanum on the nexus of the anterior byssus retractor muscle of Mytilus edulis L.

The nexus of the anterior byssus retractor muscle (ABRM) of Mytilus has been observed with freeze-fracture techniques. Pits appear in the EF face and particles in the PF face, designating it as an A-type nexus. Under control conditions (lanthanum-free) the center-to-center spacing of pits and particles ranged from 14.0 nm to 15.5 nm. When lanthanum chloride (5 mM) was used in incubation media before fixation and glycerination, marked changes in the nexal membrane were observed. These changes involved close packing and long-range ordering of pits in the EF face, as shown by optical diffraction. In the presence of lanthanum the center-to-center spacing of the pits was 11.7 nm, while the particles remained at a spacing of 15.0 nm. From this we conclude that specific agents can alter the array of pits and particles in a nexus (gap junction).

Animals↗