Proposed model for the flagellar rotary motor with shear stress transmission.

Most bacteria that swim are propelled by flagellar filaments, which are driven by a rotary motor powered by proton flux. The motor consists of the rotor and the stator. The stator consists of about 8 MotA-Mot B complex. There seems to be no definite information about the structure between the rotor and the stator, and it is examined whether the experimental data can be explained based upon the following assumptions. (a) There is viscoelastic medium between the rotor and the stator. (b) MotA-MotB complex has an electric dipole moment and produces shear stress in the electric field by a proton in the channel. Calculation results based upon these assumptions are in good agreement with the following experimental observations. (1) One revolution of the flagellar rotation consists of a constant number of steps. (2) The rotation velocity of the rotor is proportional to the trans-membrane potential difference. (3) When the rotational velocity of a flagellum is changed by adjusting the viscosity of the outer fluid, the torque for the cell to rotate a flagellum is practically constant but sharply decreases when the rotational velocity increases over a critical value. (4) The rotation direction remains the same when the sign of the electrochemical potential gradient is reversed. (5) The cell produces constant torque to rotate the flagellum even when the cell is rotated by externally applied torque. (6) A simple switch mechanism is proposed for chemotaxis.

Theory of muscle contraction mechanism with cooperative interaction among crossbridges.

The power stroke model was criticized and a model was proposed for muscle contraction mechanism (Mitsui, 1999). The proposed model was further developed and calculations based on the model well reproduced major experimental data on the steady filament sliding (Mitsui and Ohshima, 2008) and on the transient phenomena (Mitsui, Takai and Ohshima, 2011). In this review more weight is put on explanation of the basic ideas of the model, especially logical necessity of the model, leaving mathematical details to the above-mentioned papers. A thermodynamic relationship that any models based upon the sliding filament theory should fulfill is derived. The model which fulfills the thermodynamic relationship is constructed on the assumption that a myosin head bound to an actin filament forms a complex with three actin molecules. In shortening muscles, the complex moves along the actin filament changing the partner actin molecules with steps of about 5.5 nm. This process is made possible through cooperative interaction among cross-bridges. The ATP hydrolysis energy is liberated by fraction at each step through chemical reactions between myosin and actin molecules. The cooperativity among crossbridges disappears in length-clamped muscles, in agreement with experimental observations that the cross-bridge produces force independently in the isometric tetanus state. The distance of the head movement per ATP hydrolysis cycle is expected to be about 5.5 nm or a few times of it under the condition of the in vitro single head experiments. Calculation results are surveyed illustrating that they are in good agreement with major experimental observations.

Remarks on muscle contraction mechanism II. Isometric tension transient and isotonic velocity transient.

Mitsui and Ohshima (2008) criticized the power-stroke model for muscle contraction and proposed a new model. In the new model, about 41% of the myosin heads are bound to actin filaments, and each bound head forms a complex MA(3) with three actin molecules A1, A2 and A3 forming the crossbridge. The complex translates along the actin filament cooperating with each other. The new model well explained the experimental data on the steady filament sliding. As an extension of the study, the isometric tension transient and isotonic velocity transient are investigated. Statistical ensemble of crossbridges is introduced, and variation of the binding probability of myosin head to A1 is considered. When the binding probability to A1 is zero, the Hill-type force-velocity relation is resulted in. When the binding probability to A1 becomes finite, the deviation from the Hill-type force-velocity relation takes place, as observed by Edman (1988). The characteristics of the isometric tension transient observed by Ford, Huxley and Simmons (1977) and of the isotonic velocity transient observed by Civan and Podolsky (1966) are theoretically reproduced. Ratios of the extensibility are estimated as 0.22 for the crossbridge, 0.26 for the myosin filament and 0.52 for the actin filament, in consistency with the values determined by X-ray diffraction by Wakabayashi et al. (1994).

Remarks on muscle contraction mechanism.

Muscle contraction mechanism is discussed by reforming the model described in an article by Mitsui (Adv. Biophys. 1999, 36, 107-158). A simple thermodynamic relationship is presented, which indicates that there is an inconsistency in the power stroke model or the swinging lever model. To avoid this difficulty, a new model is proposed. It is assumed that a myosin head forms a polaron-like complex with about three actin molecules when it attaches to an actin filament and the complex translates along the actin filament producing force. Various experimental data on the muscle contraction are well explained based upon the model.

Shear stress transmission model for the flagellar rotary motor.

Most bacteria that swim are propelled by flagellar filaments, which are driven by a rotary motor powered by proton flux. The mechanism of the flagellar motor is discussed by reforming the model proposed by the present authors in 2005. It is shown that the mean strength of Coulomb field produced by a proton passing the channel is very strong in the Mot assembly so that the Mot assembly can be a shear force generator and induce the flagellar rotation. The model gives clear calculation results in agreement with experimental observations, e g., for the characteristic torque-velocity relationship of the flagellar rotation.

Proposed model for the flagellar rotary motor.

Flagellated bacteria swim by rotating helical filaments driven by motors embedded in the cell wall and cytoplasmic membrane. A model is proposed to explain the mechanism of the motor. The protons passing through the channels induce a strong electric field in Mot molecules. This field originates an impulse force to cause the flagellar rotation if the following conditions are fulfilled: (a) Mot molecules have a spontaneous electric polarization. (b) The lipid bilayers are viscoelastic. (c) There is a delay of deformation in response to stress in Mot molecules. The conclusions driven from the model are in agreement with the following experimental observations, denoting the flagellar rotation velocity as omega. (1) The torque is practically constant independent of omega from 0 to a critical value omega(cr) and then decreases sharply. (2) When omega is smaller than omega(cr), the torque varies little with temperature. (3) The critical velocity omega(cr) shifts to lower speed at lower temperatures. (4) Where omega is larger than omega(cr), declining of the torque steepens at lower temperatures. (5) When omega is smaller than omega(cr), one revolution of the flagellar rotation consists of a constant number of steps. (6) When omega is smaller than omega(cr), omega is proportional to the transmembrane potential difference. (7) The stator produces constant torque even when the stator is rotated relative to the rotor by external forces. (8) How the flagellar rotation velocity changes when the direction of the proton passage is reversed. (9) The motor has a switch that reverses the sense of the flagelllar rotation with the same absolute value of torque.

High-frequency QRS potentials as a marker of myocardial dysfunction after cardiac surgery.

BACKGROUND: High-frequency QRS potentials are sensitive to myocardial ischemia. The aim of this study was to evaluate the usefulness of high-frequency QRS potentials as a marker of myocardial dysfunction after cardiac surgery. METHODS: Seventy patients undergoing coronary artery bypass grafting or heart valve surgery were involved. High-frequency QRS potentials were measured by signal-averaged electrocardiogram, and calculated as the root-mean-square voltage of the total QRS duration (RMST). The postoperative RMST was expressed as a percentage of the preoperative RMST. The mean RMST at 1 to 2 hours after removing the aortic cross-clamp was compared with the cardiac index, inotropic agents, and aortic cross-clamping time. The occurrence of ventricular tachycardia within 24 hours and the RMST at 2 postoperative days were also evaluated. Patients were divided into quartile groups from highest to lowest at postoperative RMST (groups 1, 2, 3, and 4, respectively, from maximum to minimum). RESULTS: In postoperative states, cardiac index significantly decreased in accordance with the RMST decrease in a stepwise manner, although there were no differences in cardiac index among the four groups preoperatively. Inotropic agents and aortic cross-clamping time increased as RMST decreased. A high rate of ventricular tachycardia within 24 hours and delayed RMST recovery at 2 postoperative days were seen in group 4. The curve of sensitivity and specificity showed that severe reduction (threshold, 35%) of RMST indicated low-output syndrome. CONCLUSIONS: The severe reduction of filtered high-frequency QRS potentials was related to myocardial dysfunction. Measurement of filtered high-frequency QRS potentials could become a useful, noninvasive, real-time monitor of myocardial dysfunction after surgery.

Visualization of atrial excitation by magnetocardiogram.

We tried to visualize normal atrial excitatory process by magnetocardiogram (MCG) measured from both anterior chest and back using our newest multi-channel SQUID system. Twenty normal subjects were studied. After measuring the normal (B(z)) component of the magnetic field, we constructed an isomagnetic and vector arrow map from spatial derivatives of the normal (B(z)) component in the tangential direction. By the MCG measurement from the anterior chest, current arrows were recognized in the right upper portion which were directed to the left lower from the beginning of the P wave to the P-wave peak. By the measurement from the back, current arrows were able to be visualized in the right to middle upper portion which were directed to the left or left lower just before the P-wave peak. We conclude that we successfully recognized the right atrial excitation and its spread to the left atrium and observed the time course of normal atrial excitatory process by the MCG measurement from not only anterior chest but also back using 64-channel SQUID system.

Intrabronchial orthotopic propagation of human lung adenocarcinoma--characterizations of tumorigenicity, invasion and metastasis.

Using the intrabronchial orthotopic propagation method, we evaluated the biological characteristics of human adenocarcinoma cell lines in vivo and examined the expressions of matrix metalloproteinase-2 (MMP-2) and -9 (MMP-9) and their related proteins. Nine human lung adenocarcinoma cell lines, including A549, NCI-H23, NCI-H322, NCI-H358, Calu-3, PC-14, LC-2/ad, RERF-LC-KJ and PL16T, were injected into the peripheral bronchi of mice using this method. The mice were sacrificed at 4 and 8 weeks after tumor cell propagation and the lungs and other organs were observed macroscopically and histologically. We classified the adenocarcinoma cell lines, according to their intrapulmonary tumorigenicity, into the following three groups: (A) those that showed a high incidence of intrapulmonary implantation (>50%) (A549 and NCI-H358). A549 showed mediastinal lymph node metastasis and pleural dissemination; (B) those that showed a low incidence of intrapulmonary implantation (PC-14, NCI-H322, NCI-H23, Calu-3, and LC-2/ad); (C) those that showed no tumorigenicity in the lung (RERF-LC-KJ and PL16T). In order to characterize the biological differences between each cell line, we investigated the expressions of MMP-2 and MMP-9 and their related molecules by northern blot analysis. The expressions of MMP-2 and MMP-9 and their activators (membrane-type 1-MMP and urokinase-type plasminogen activator) were thought to be associated with the growth, invasion and metastasis of the human lung adenocarcinoma cell lines examined.