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R J Baskin

Publications and source records attributed to R J Baskin.

At least 37 records · Page 2Linked to original sources
PubMed1988

Theory of optical ellipsometric measurements from muscle diffraction studies.

A theory of optical ellipsometry describing the complete phase shift and ellipticity of light diffracted from a single muscle fiber is developed. We show that both the phase shift information, described commonly by the birefringence of the fiber, and the ellipticity information, described by the differential polarizability ratio, are necessary to provide a complete picture of the complex contributions to the total optical anisotropy spectra from a diffraction pattern derived from the striated muscle cell. Both form and intrinsic contributions play significant roles in either the birefringence measurement or the differential field ratio measurement. However, we show that their relative weights in these two measured quantities are different, and measuring both of these parameters is necessary to obtain a more complete assessment of the cross-bridge structure and dynamics. The theoretical results have been tested for three different situations: solvent index matching, passive stretch of a resting fiber, and cross-bridge changes under isometric conditions. Comparisons between experimental data and simple model calculations provide much information regarding cross-bridge orientation and structure.

Animals↗
PubMed1987

Optical ellipsometry on the diffraction order of skinned fibers. pH-induced rigor effects.

The polarization properties of light diffracted from single-skinned fibers of skeletal muscles have been examined under conditions in which the bathing solution pH and the ionic strength are changed. For fibers in the relaxed state, we observe large decreases in both the total depolarization signal, r, and the total diffraction birefringence signal, delta nT, upon pH change from 7.0 to 8.0 at normal ionic strength. However, if the ionic strength is raised, then the r-value change as the pH changes from pH 7.0 to pH 8.0 is much smaller. If the rigor state is achieved at pH 8.0, and 0 mM ATP under either of the ionic strength conditions, the fiber can still be stretched. Rigor stiffness for this state is only approximately 20% that of the value of the stiffness at pH 7.0 rigor. Electron micrographs obtained under this pH 8.0 rigor state show that the overlap region can be decreased upon stretching the fiber, signifying a different kind of weaker-binding rigor state. Optically, the weaker-binding rigor state has a lower depolarization signal and larger form birefringence than the strong-binding rigor state. To convert from one type of rigor state (pH 7.0) to the other rigor state (pH 8.0), or vice versa, the fiber must first be relaxed. Apparently, either of the rigor states can block the full impact of the pH effect.

Animals↗
PubMed1986

Light diffraction patterns and sarcomere length variation in striated muscle fibers of Limulus.

Light diffraction patterns produced by Limulus striated muscle fibers were examined. Segments of fibers were glycerinated, fixed or bathed in relaxing solution. Profiles of the intensity of a diffracted order vs. the angle of incidence of the laser beam often exhibited narrow peaks with the fiber at rest length. The incident angles at which the intensity of left and right orders is greatest are used to calculate the sarcomere length, supporting the notion that regions of the fiber are organised into Bragg reflecting planes. These profiles developed subpeaks and broadened upon stretch of the fiber. The broad angle scan profiles are suggested to result from a decrease in the regular packing of myofibrils as the fiber is lengthened. The angular width of the subpeaks is used to estimate the thickness of clusters of myofibrils. The variation in sarcomere length along the fiber, as determined by the 0th to 1st diffraction order spacing, was dependent upon the fiber preparation. Glycerinated fibers and those bathed in relaxing solution showed more variation than fixed fibers. The variation of sarcomere length is compared to the variation in thick filament lengths in Limulus reported by Dewey et al. (1982). These results are compared to those obtained from frog fiber segments.

Animals↗
PubMed1986

Optical depolarization changes in single, skinned muscle fibers. Evidence for cross-bridge involvement.

Optical ellipsometry studies of single, skinned muscle fibers conducted on the diffraction orders have yielded spectra that are sensitive to the state of the fiber. The linearly polarized light field vector becomes elliptically polarized as it passes through the fiber and may be collected at the diffraction orders. Fibers that have been subjected to extraction of myosin (0.6 M KCl) retain a weak diffraction pattern and exhibit a substantially decreased depolarization of incident linearly polarized light. A significant decrease in polarization is seen in skinned fibers that are subject to an increase in pH from 7.0 to 8.0. This increase in pH results in a decrease of approximately 30% in the depolarization angle of single fibers. The major decrease in depolarization angle that we observe at pH 8.0 is consistent with the notion that as cross-bridges move out from the shaft of the thick filament, their ability to cause depolarization of the incident linearly polarized light decreases. This interpretation is also consistent with the work of Ueno and Harrington where the decrease in the ability to cross-link S-1 and S-2 to the thick filament at pH 8.2 suggests cross-bridge movement away from the thick filament. A large decrease in birefringence, seen after treatment of skinned fibers with alpha-chymotrypsin, appears to be related to the breakdown of myosin into rod, S-1, heavy meromyosin, and light meromyosin.

Adenosine Triphosphate↗
PubMed1985

Depolarization spectrum of diffracted light from muscle fiber. The intrinsic anisotropy component.

The depolarization signal of the diffraction patterns from muscle fibers includes information that differs from that of transmission birefringence experiments. Although both the birefringence studies and the phase shift studies of Yeh et al. (Yeh, Y, and G. Pinsky, 1983, Biophys. J., 42:83-90; Yeh, Y., M. E. Corcoran, R. J. Baskin, and R. L. Lieber, 1983, Biophys. J., 44:343-351) include inseparable intrinsic and form contributions, the present analysis shows that the magnitude of the E-field components of diffracted light is affected only by the intrinsic contribution. We have analyzed the amplitude portion of the data of which the phase shift portion had previously been reported (Yeh, Y., M. E. Corcoran, R. J. Baskin, and R. L. Lieber, 1983, Biophys. J., 44:343-351). For the relaxed-to-rigor transition, these field amplitudes also exhibit changes when ATP concentration is decreased. The observed decrease in optical depolarization upon rigor is consistent with the idea that optically anisotropic elements move away from the myosin thick filament under such conditions.

Adenosine Triphosphate↗
PubMed1984

Stereological analysis of transverse tubules and sarcoplasmic reticulum isolated from normal and dystrophic skeletal muscle.

Vesicles isolated from the transverse tubules and sarcoplasmic reticulum of normal and dystrophic chicken skeletal muscle were analyzed for enzymatic activity and examined following freeze-fracture. A stereological procedure was used to determine particle density distributions on the resulting membrane fracture faces. The particle densities measured in this investigation were compared with those of an earlier study on intact muscle. Isolated sarcoplasmic reticulum vesicles showed a characteristically high P-face (cytoplasmic leaflet) particle density (5108 +/- 169 particles/micron2) and a low E-face (luminal leaflet) particle density (505 +/- 57 particles/micron2). Transverse tubule fractions showed a high E-face particle density (2346 +/- 179 particles/mu2) as well as a substantial P-face particle density (1019 +/- 129 particles/micron2). The high transverse tubule E-face particle density represents a characteristic morphological feature in the same way that the very high P-face particle density is characteristic of sarcoplasmic reticulum membranes. The major morphological alteration in dystrophic membranes was a shift in the E-face particle density distribution of isolated transverse tubules to a lower average particle density. (The E-face particle density of sarcoplasmic reticulum fractions showed no differences.)

Adenosine Triphosphatases↗
PubMed1984

Sarcomere length determination using laser diffraction. Effect of beam and fiber diameter.

An experimental and theoretical analysis is presented involving the effect of variation in fiber and beam diameter upon the determination of average sarcomere length in isolated single muscle fibers using laser light diffraction. The muscle diffraction phenomenon is simplified by first considering diffraction order position and intensity to be the result of grating and Bragg diffraction. It is the product of the intensity profiles, which results from these types of diffraction, that produces the diffracted order. These simplifying assumptions are then extended to the case of the real muscle. Based on these considerations and the theory that we recently presented, conditions are set forth under which grating information (i.e., sarcomere length) can be maximally expressed to yield accurate average sarcomere length values.

Animals↗
PubMed1983

Calcium transport, ATPase activity and lipid composition in sarcoplasmic reticulum isolated from isogenic lines of normal and dystrophic chickens.

Two new lines of chickens with near identical genotypes (greater than 90% isogeneity), one demonstrating avian dystrophy, were used for isolation of sarcoplasmic reticulum vesicles. Vesicles from line 433 (dystrophic) displayed reduced Ca2+-ATPase activity, phosphoenzyme formation and steady-state calcium transport capabilities in comparison with vesicles from line 03 (normal). Lipid analyses show that dystrophic vesicles have greater amounts of cholesterol and lesser amounts of phosphatidylcholine. The results support the use of isogenic chickens in further studies of avian dystrophy. However, the results also suggest that current sarcoplasmic reticulum vesicle purification procedures dependent on differential calcium accumulation may not fully achieve the intended purpose.

Animals↗
PubMed1983

Optical depolarization changes on the diffraction pattern in the transition of skinned muscle fibers from relaxed to rigor state.

Light diffraction spectra from single or small bundles of skinned striated muscle fibers show large changes in polarization properties when muscles are placed into rigor. The technique of combining optical diffraction and ellipsometry measurements has previously been shown by Yeh and Pinsky to be a sensitive probe of periodic anisotropic regions of the fiber. In the present work, using this method, the observed spectrum shows marked decrease in the measured phase angle, delta, as the fiber approaches the rigor state. The degree of phase angle change is a function of sarcomere length: Maximum overlap of approximately 2.3 microns gives the most change in delta a delta delta R-R approximately 35 degrees decrease for a bundle of three fibers. At a sarcomere length of 2.9 microns this delta delta R-R value is only 10 degrees. At a nonoverlapping length of approximately 3.8 microns, delta does not vary at all upon the removal of ATP. The rigor state was confirmed by stiffness measurements made after small-amplitude (0.75%), quick length changes. Upon re-relaxation, the stiffness of the skinned fiber decreased to the value of the resting state (4 mM ATP) and the phase angle delta returned to its original value. A model based on either anisotropic subunit-2 (S-2) movements or other cross-bridge-related structural anisotropy (form birefringence) changes during the relaxed-rigor transition is suggested.

Adenosine Triphosphate↗
PubMed1983

Intersarcomere dynamics of single muscle fibers during fixed-end tetani.

The contraction dynamics of end and center regions of single fibers have been measured during fixed-end tetani. Experimental control and data acquisition are provided by a digital system that can acquire diffraction data as fast as every 260 microseconds for 300-700 ms. Tension records are simultaneously displayed on a storage oscilloscope. Resting sarcomere length variation between the end and center regions was analogous to that of Gordon et al. (1966). During the rapid rise in force (less than 45 ms), the end regions contract almost twice as fast as the center regions. During the slow rise in force, the velocity of contraction of the end regions was 3.8 times the velocity of stretch of the center regions. In addition, factors that affected the rate and extent of the slow rise in tension also affected the rate and extent of end shortening. In 58% of the cases studied, the amount of shortening observed in the end region was enough to explain the extent of the slow rise in tension. These data support the explanation of creep first proposed by A. V. Hill (1953) and used by Gordon et al. (1966) to justify their use of the back-extrapolation technique in measuring the isometric force-generating capability of a single fiber. These data also indicate that the laser diffraction technique may provide an effective, noninvasive method for studying sarcomere dynamics during creep and related phenomena.

Animals↗
PubMed1981

Enzymatic activity of dystrophic chicken sarcoplasmic reticulum.

We have isolated sarcoplasmic reticulum from normal and dystrophic chicken muscle, using an improved isolation procedure. Dystrophic sarcoplasmic reticulum has a reduced level of calcium-sensitive ATPase activity, phosphoenzyme formation, and steady-state calcium transport. Anion-stimulated calcium transport by dystrophic sarcoplasmic reticulum is also reduced when measured under the proper conditions, and dystrophic sarcoplasmic reticulum shows no alteration in calcium efflux rate. Active calcium phosphate loading of the normal and dystrophic sarcoplasmic reticulum preparations indicates that a reduced percentage jof the dystrophic vesicles are capable of active calcium transport. The loaded dystrophic sarcoplasmic reticulum vesicles exhibit the same relative reductions in enzymatic activity as the starting sarcoplasmic reticulum preparations. However, the enzyme activities of normal and dystrophic sarcoplasmic reticulum are similar in the presence of detergent and exogenous phospholipid. On the basis of these results, we suggest that the lipid microenvironment of the dystrophic enzyme is altered.

Animals↗
PubMed1981

Light diffraction studies of active muscles fibres as a function of sarcomere length.

This investigation has established the following points. (1) Activation of single intact frog muscle fibres or mechanically skinned fibres results in a decrease in the intensity of the first-order line at all sarcomere lengths at which filament overlap is present. (2) At long sarcomere lengths (greater than 3.6 micrometers) the intensity decrease upon stimulation of intact fibres diminishes until above 3.9 micrometers no decrease is seen. In the skinned preparation, no intensity change is seen at sacromere lengths above 3.6 micrometers. (3) The intensity decrease seen in the intact fibres in the 3.6-3.9 micrometers sarcomere length region may be due to contraction of sarcomeres near the tendons, which have a shorter sarcomere length than those illuminated by the laser beam, and thus may not be stretched beyond filament overlap. (4) No intensity decrease is observed upon activation at very long (greater than 4.5 micrometers) sarcomere lengths. (5) Mechanically skinned fibres show a graded intensity response to free calcium. (6) Scans of first-order line width show no broadening upon activation, indicating that sarcomere length dispersion in the illuminated region of the fibre does not increase.

Animals↗
PubMed1981

Activation of the contractile system in crustacean muscle: ultrastructural evidence for the role of the T system.

Freeze-fracture and thin sections of lobster abdominal fast flexor muscle were used to study the morphology of the sarcoplasmic reticulum (SR) and T system of crustacean muscle. Tannic acid mordanting, which can result in a dense black deposit in the T system lumen, was used to distinguish T system from SR membranes. Ferritin was also used as an extracellular tracer to confirm the tannic acid method. The T system consists of an extensive network of flattened sacs which fills most of the space between the myofibrils and is in close contact with them. The SR also appears as flattened sacs, sometimes with fenestrations. There is extensive junctional contact between the SR and T system. Quantitative estimates of the volume and surface area of the membranes show that the T system has about 50% more surface area than the SR. The intramembrane particle (IMP) density of the PF face of the T system is about 1100/micron 2 membrane, while the IMP density of the PF face of SR is about 4800/micron 2 membrane. In morphology, extent, and IMP density, the T system of lobster abdominal fast flexor muscle appears (AFF) adapted to provide at least part of the Ca2+ for muscle activation and the transport system for relaxation.

Animals↗
PubMed1981

Intensity of light diffraction from striated muscle as a function of incident angle.

In a recently developed theory of light diffraction by single striated muscle fibers, we considered only the case of normal beam incidence. The present investigation represents both an experimental and theoretical extension of the previous work to arbitrary incident angle. Angle scan profiles over a 50 degrees range of incident angle (+25 degrees to -25 degrees) were obtained at different sarcomere lengths. Left and right first-order scan peak separations were found to be a function of sarcomere length (separation angle = 2 theta B), and good agreement was found between theory and experiment. Our theoretical analysis further showed that a myofibrillar population with a single common skew angle can yield an angle scan profile containing many peaks. Thus, it is not necessary to associate each peak with a different skew population. Finally, we have found that symmetry angle, theta s, also varies with sarcomere length, but not in a regular manner. Its value at a given sarcomere length is a function of a particular region of a given fiber and represents the average skew angle of all the myofibril populations illuminated. The intensity of a diffraction order line is considered to be principally the resultant of two interference phenomena. The first is a volume-grating phenomenon which results from the periodic A-I band structure of the fiber (with some contribution from Z bands and H zones). The second is Bragg reflection from skew planes, if the correct relation between incident angle and skew angle is met. This may result in intensity asymmetry between the left and right first order lines.

Animals↗
PubMed1980

Theory of light diffraction by single skeletal muscle fibers.

A theoretical discussion is presented describing the diffraction of laser light by a single fiber of striated muscle. The complete three-dimensional geometry of the fiber has been taken into consideration. The basic repeated unit is taken as the sarcomere of a single myofibril, including its cylindrical geometry. The single fiber is considered as the sum of myofibrils up to the fiber dimensions. When proper phasing is taken into account, three cases of interest are analyzed. (a) When the adjacent myofibrils are totally aligned with respect to their index of refraction regions (e.g., A and I bands), then the diffraction pattern reflects that of a larger striated cylinder with the dimensions of the fiber. (b) When a particular skew plane develops for the myofibril elements, additional Bragg reflection occurs at certain specific sarcomere lengths, and intensity asymmetry amongst the diffracted orders occurs. (c) When the myofibril phasing changes in a random fashion, while all sarcomeres remain at the same length, then intensity decrease is directly related to the phase deviation from a reference phase point. This condition may well describe a fiber undergoing active isometric contraction.

Chemical Phenomena↗