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Biomedical subjects

F D Carlson

Publications and source records attributed to F D Carlson.

16 recordsLinked to original sources
PubMed1992

A quasi-elastic light scattering study of smooth muscle myosin in the presence of ATP.

We have investigated the hydrodynamic properties of turkey gizzard smooth muscle myosin in solution using quasi-elastic light scattering (QELS). The effects of ionic strength (0.05-0.5 M KCl) and light chain phosphorylation on the conformational transition of myosin were examined in the presence of ATP at 20 degrees C. Cumulant analysis and light scattering models were used to describe the myosin system in solution. A nonlinear least squares fitting procedure was used to determine the model that best fits the data. The conformational transition of the myosin monomer from a folded form to an extended form was clearly demonstrated in a salt concentration range of 0.15-0.3 M KCl. Light chain phosphorylation regulates the transition and promotes unfolding of the myosin. These results agree with the findings obtained using sedimentation velocity and electron microscopy (Onishi and Wakabayashi, 1982; Trybus et al., 1982; Trybus and Lowey, 1984). In addition, we present evidence for polymeric myosin coexisting with the two monomeric myosin species over a salt concentration range from 0.05 to 0.5 M KCl. The size of the polymeric myosin varied with salt concentration. This observation supports the hypothesis that, in solution, a dynamic equilibrium exists between the two conformations of myosin monomer and filaments.

Adenosine Triphosphate↗
PubMed1989

Form birefringence of muscle.

We investigate the sensitivity of measurements of muscle birefringence to cross-bridge dynamics in the resting, active, and rigor states. The theory of form birefringence is reviewed, and an optical model is constructed for the form birefringence of muscle. Values for the parameters in the model are selected or deduced from the literature. As an illustration of the use of the model, plausible distributions for the orientations of cross-bridges in the resting, active, and rigor states are constructed using a model for cross-bridge dynamics suggested by Huxley and Kress (1985). The general magnitude of the predictions of our model is comparable with that of published measurements of muscle birefringence. However, the precise values of the predicted birefringence for the resting, active, and rigor states are sensitive to the assumed orientations of cross-bridges. We also investigate the dependence of muscle birefringence on sarcomere length and on disorder in the orientation of the myofilament array. We conclude that measurements of muscle birefringence can play a useful role in distinguishing between proposed models of cross-bridge dynamics.

Actin Cytoskeleton↗
PubMed1987

Quasi-elastic light scattering studies of membrane motion in single red blood cells.

Studies of red blood cells (RBCs) and RBC ghosts, using a quasi-elastic light scattering (QELS) microscope spectrometer, have identified the membrane as the primary source of the light scattering signal. This is the first report in which motion of the cell membrane has been demonstrated to be the primary source of the QELS signal from a cell. Cytoplasmic changes induced in the RBC by varying the osmotic strength of the medium were also detected using this technique. Comparison of the data from white blood cells (WBCs) with the RBC data demonstrated significant differences between different types of cells.

Cytoplasm↗
PubMed1975

The interaction of heavy meromyosin and subfragment 1 with actin. Physical measurements in the presence and absence of adenosine triphosphate.

Viscosity, turbidity, and laser-light fluctuation autocorrelations of acto-heavy merymyosin (HMM) and acto-subfragment 1 (S-1) solutions were measured under conditions where the actin-activated ATPase is close to its maximal value. The results were compared to similar data obtained in the absence of ATP where the actin and myosin fragments were completely domplexed, and in the presence of ATP but at 0.1 M KLC where the actin and HMM or S-1 were almost completely dissociated. It was found that at maximal actin activation, the viscosity, turbidity, and autocorrelation data were all much closer to the values for the completely dissociated systems than to the values for the completely complexed systems. Assuming that viscosity, turbidity, and autocorrelation measurements approximate a linear measure of binding between actin and HMM or S-1, the results suggest that at maximal actin activation less than 10% of the HMM or S-1 are bound to the actin. Therefore as was suggested previously by ultracentrifuge and kinetics studies, it appears that under conditions of maximal actin activation, most of the HMM and S-1 occur in a refractory state unable to bind to actin.

Actins↗
PubMed1975

Structural fluctuations in the steady state of muscular contraction.

Recent studies of the intensity fluctuation spectra of coherent light scattered from striated muscle have demonstrated the existence of large scale fluctuations in position and polarizability at the level of the myofibrillar sarcomere and its major structural subunits during the steady state of contraction. The existence of these fluctuations implies a fluctuating driving force. Various possible fluctuating motions of the thick and thin filaments, A and I bands, and entire sarcomeres are described. The magnitude of the fluctuating forces associated with the making and breaking of cross bridges is estimated. A mechanical model is proposed for coupling structural elements of a single sarcomere to one another and for coupling myofibrillar sarcomeres to one another. It is shown that the fluctuating force generated by the spontaneous making and breaking of cross bridges in conjunction with the model accounts for some of the features of the observed intensity fluctuation spectra.

Animals↗
PubMed1975

Structural dynamics of frog muscle during isometric contraction.

Intensity fluctuation autocorrelation functions of laser light scattered by actively contracting muscle were measured at points in the scattered field. They were reproducible and showed characteristics which depended on the physiological state of the muscle and the parameters of the scattering geometry. The autocorrelation functions had large amplitudes and decay rates that varied significantly with the phase of the contraction-relaxation cycle. The dependence of the autocorrelation function on scattering geometry indicated many elements with diameters on the order of 0.5 mum (presumed to be myofibrillar sarcomeres or their A bands or I bands) undergo independent random changes in their axial positions and their internal distribution of optical polarizability during the plateau of an isometric tetanus. The experimental results are interpreted in terms of a model in which most of the scattering elements in isometrically contracting muscle have random fluctuating axial velocities of average magnitude 20 nm/ms that persist for a few milliseconds at least. In addition to these axial motions there are local fluctuations in polarizability. Similar intensity fluctuation autocorrelation functions were observed throughout the active state on two muscle preparations, whole sartorius muscle and small bundles of single fibers (three to eight) of semitendinosus muscle. These results imply that the tension developed during an isometric tetanus contains a fluctuating component as well as a constant component.

Animals↗
PubMed1973

Initial heat production in isometric from muscle at 15 degrees C.

An infrared radiation-detecting system was used to measure initial heat production in bull frog sartorius muscle at 15 degrees C. Numerous tests with the system showed that thermal artifacts were not noticeable. Many previous measurements with myothermic thermopiles were corroborated with this method. In addition, a cooling phase as large as 0.39 of peak exothermicity was found during and after relaxation. Cooling diminished with both increasing sarcomere length and increasing duration of mechanical activity. No large rapid increase in heat rate accompanied a 0.6 reactivation at the peak of twitch tension. Above rest length, initial heat rate and the heat produced up to the peak of tension decreased nearly proportionally with overlap of myofilaments, while the total twitch initial heat decreased slightly.

Animals↗
PubMed1971

Transient phases of the isometric tetanus in Frog's striated muscle.

In an isometric tetanus in frog's sartorius muscle tension approaches the plateau exponentially with rate constant alpha. alpha a depends on sarcomere length, s, and temperature, T, according to the Arrhenius equation See PDF for Equation for temperatures between 1 and 20 degrees C and for sarcomere lengths 2.0-2.8 microm. The energy of activation, E, does not vary significantly with s; E = 13.9 +/- 2.4 kcal/mole. A(s) decreases monotonically with s; A(2.1 microm) is about three times greater than A(2.8 microm). Late in relaxation active tension approaches zero exponentially with rate constant r. r decreases exponentially with increasing duration of tetanus, D, from r(0) in a twitch to r(infinity) for large D. The rate constant for decrease of r with D increases with s and with T. r(0) and r(infinity) obey the Arrhenius equation and decrease with increasing s.

Animals↗
PubMed1969

Translational and rotational diffusion constants of tobacco mosaic virus from Rayleigh linewidths.

The translational and rotational diffusion constants of tobacco mosaic virus (TMV) have been determined from homodyne and heterodyne measurements of the spectrum of laser light scattered from dilute aqueous solutions of TMV. Our results for the translational and rotational constants respectively, reduced to 20 degrees C, are: D(T) = 0.280 +/- 0.006 x 10(-7) cm(2)/sec, and D(R) = 320 +/- 18 sec(-1). We include a theoretical derivation of the spectrum of light scattered from rod-shaped molecules which reproduces results obtained previously by Pecora, but which is specialized at the outset to the problem of dilute solutions so that simple single-particle correlation functions may be utilized. An analysis of the photocurrent spectrum for both the homodyne and heterodyne detection schemes is given. Various data reduction schemes utilized in the analysis of our spectra are described in some detail, and our results are compared with values of the diffusion constants obtained from other experiments.

Biophysical Phenomena↗
PubMed1967

The relation between heat produced and phosphorylcreatine split during isometric contraction of frog's muscle.

1. Heat production, tension development and phosphorylcreatine (PC) splitting have been measured simultaneously during isometric contractions of iodoacetate-poisoned frogs' sartorii at 0 degrees C. The muscles were stimulated to produce a series of 30 twitches or a 10 sec tetanus or a 30 sec tetanus.2. Of the several possible methods of calculating PC breakdown the best appears to be the one based on the assumption that PC/(total creatine) was originally the same in the two muscles of a pair.3. The difficulty of expressing PC break-down, heat production etc. in terms of the muscle's size is demonstrated.4. Several artifacts are discussed, including the heat produced by the stimulus and the possible role of reactions other than PC splitting.5. Even when these have been substantially eliminated there remains the rather intractable statistical problem of establishing a functional relationship between heat produced and PC split when both of these variables contain errors, so that ordinary regression analysis is misleading. It is shown that this problem can be dealt with satisfactorily by introducing other instrumental variables that can be determined experimentally.6. The final conclusion is that the in vivo enthalpy of hydrolysis of PC is about 10.6 kcal/mole, and is the same in twitches and in tetani.

Animals↗