ABSTRACT
We examined the roles of inertial (e(3)), shoulder-centre of mass (SH-CM) and shoulder-elbow articular (SH-EL) rotation axes in the non-visual control of unconstrained 3D arm rotations. Subjects rotated the arm in elbow configurations that yielded either a constant or variable separation between these axes. We hypothesized that increasing the motion frequency and the task complexity would result in the limbs' rotational axis to correspond to e(3) in order to minimize rotational resistances. Results showed two velocity-dependent profiles wherein the rotation axis coincided with the SH-EL axis for S and I velocities and then in the F velocity shifted to either a SH-CM/e(3) trade-off axis for one profile, or to no preferential axis for the other. A third profile was velocity-independent, with the SH-CM/e(3) trade-off axis being adopted. Our results are the first to provide evidence that the rotational axis of a multi-articulated limb may change from a geometrical axis of rotation to a mass or inertia based axis as motion frequency increases. These findings are discussed within the framework of the minimum inertia tensor model (MIT), which shows that rotations about e(3) reduce the amount of joint muscle torque that must be produced by employing the interaction torque to assist movement.
Subject(s)
Arm/physiology , Movement/physiology , Posture/physiology , Rotation , Biomechanical Phenomena , Female , Humans , Male , Muscle, Skeletal/physiology , Proprioception , Torque , Young AdultABSTRACT
The relaxation rate R = pi Delta nu(1/2) of the quadrupolar (23)Na nucleus was measured at pH approximately 7 using a 200 MHz NMR spectrometer with a view to observe the interaction between hyaluronan and its natural counterion Na(+) and the bications Ca(++), Mg(++) and Cu(++). An interpretation of our results, by means of the "entropy of fluctuations" concept of Na(+), is presented. We show that Cu(++) ions are more effective than Ca(++) and Mg(++). A possible model of complexation of Cu(++) in a cage formed by the 1-4 glycosidic bond, the carboxylate side-chain and the acetoamide side-chain is proposed, according to electrostatic potential computations using the ZINDO1 quantum semi empirical method.
Subject(s)
Cations, Divalent/chemistry , Hyaluronic Acid/chemistry , Calcium , Carbohydrate Conformation , Carbohydrate Sequence , Copper , Humans , Hyaluronic Acid/isolation & purification , Magnesium , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Sequence Data , Sodium , Trisaccharides/chemistry , Umbilical Cord/chemistryABSTRACT
The interaction between DNA and the platinum compounds cis-DDP, trans-DDP and TDP has been studied in aqueous solution at pH 7.0 by transient electric birefringence (TEB). Data was obtained on the electro-optical characteristics and hydrodynamic properties of these solutions. The specific interactions between each of the three platinum compounds and DNA were differentiated, and their binding affinity for DNA phosphate sites was as follows, in decreasing order of importance: TDP >> cis-DDP > trans-DDP.
Subject(s)
Birefringence , Cisplatin/metabolism , DNA/metabolism , Platinum Compounds/metabolism , Chemical Phenomena , Chemistry, Physical , Cisplatin/chemistry , DNA/chemistry , Electricity , Hydrogen-Ion Concentration , Platinum Compounds/chemistry , SolutionsABSTRACT
The interaction of calf thymus DNA with cis-DDP, trans-DDP and TDP was studied by 23Na NMR in aqueous solutions at pH=7.0, with Pt(II) compounds/DNA(P) (P=Phosphate) molar ratios r increasing from 0 till to 1P. 23Na NMR results are interpreted on one hand, with the help of a " two states model " with R(F) and R(B) relaxation rates, and, on the other hand, using the " entropy of fluctuations " concept developed by Lenk. We have established that, for the studied platinum compounds, the preference to interact with DNA phosphate sites -interpreted as a perturbation of the counterions environment- is in a decreasing order: TDP >> cis-DDP > trans-DDP. These results are discussed with regard to the interaction of DNA with the hard bication Mg++ and the soft bication Cu++.
Subject(s)
Cisplatin/chemistry , DNA/chemistry , Models, Molecular , Nuclear Magnetic Resonance, Biomolecular , Animals , Cattle , Cisplatin/metabolism , DNA/metabolism , Nucleic Acid Conformation , Nucleic Acid Denaturation , Sodium Radioisotopes , Solutions , TemperatureABSTRACT
DNA thermal transconformation is studied in absence and in presence of the cysteamine radioprotector, by observing the delta nu 1/2 variation of 23Na NMR peaks. The sodium state (Free or Bound) is discussed with the help of a two states model with RF and RB relaxation rates. The delta nu 1/2 behaviour during the DNA transconformation shows clearly the electrostatic interaction with cysteamine which is accompanied by an Na+ ejection out of phosphate sites. The temperature dependence of delta nu 1/2 in all cases leads to the conclusion that RBc (the average relaxation rate of sodium nuclei that remain bound in the coil state of DNA) tends to zero.
Subject(s)
Cysteamine/pharmacology , DNA , Nucleic Acid Denaturation , Radiation-Protective Agents , DNA/drug effects , Kinetics , Magnetic Resonance Spectroscopy/methods , Mathematics , Models, Theoretical , Sodium , ThermodynamicsSubject(s)
Cysteamine , DNA , Animals , Cattle , Magnetic Resonance Spectroscopy/methods , Thymus GlandABSTRACT
We here describe a simple apparatus for measuring temperature, accurate to 3/100 of a degree, which makes it possible to follow variations in the temperature of an accessible internal organ, and we also describe its application to the observation of possible changes in the temperature of a tumour of the uterine cervix, during treatment by curietherapy.
