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A rotational diffusion equation and its Green's function for a spheroidal particle such as a bacterial body, to which an actively driving but idle motor is attached, are presented. As an application of the theory, general expressions for the time-dependent fluorescence depolarization caused by such a particle have been obtained. Measurement of such depolarizalion should provide a useful tool for determination of the rate of revolution of the rotating motor attached to cell bodies such as bacteria under various solution conditions, if a fluorescent (or phosphorescent) label is attached to the motor shaft.

Chemical reactions in bacterial chemoreceptors are considered. It is shown that the model proposed by Macnab and Koshland explains the experimental facts not completely. Two modifications of the Macnab-Koshland's model are proposed in which the co-operative feedback control plays an important role.

Elongation of a helical bacterial flagellar filament in a fluid flow with one end attached to a slide glass is calculated. The flagellar filament is regarded as a coil spring. In this case, the spring constant is a function of the elastic constants of the flagellar filament. Relations between the elongation and the elastic constants are discussed.

Hydrodynamical properties of a helical tail of flagellated organisms are discussed. The tail is considered as a helical chain of 2 N +1 frictional elements. The translational and the rotatory friction coefficients and the interaction coefficient between translational and rotatory movement are calculated. Comparison with a helical cylinder model is made.

We develops a theory of the Brownian motion of a rigid helical object such as bacterial flagella. The statistical properties of the random forces acting on the helical object are discussed and the coefficients of the correlations of the random forces are determined. The averages 〈 z 2 (t)〉, 〈θ 2 (t)〉 and 〈z(t)θ(t)〉 are also calculated where z and θ are the position along and angle around the helix axis respectively. Although the theory is limited to short time interval, direct comparison with experiment is possible by using the recently developed cinematography technique.

Elongation of a helical bacterial flagellar filament subjected to fluid flow was calculated on the assumption that one end of the filament is firmly attached to a substratum. It was found that the quantity [E(d/2 pi r)2 + 2 mu] could be determined by measuring the elongation at various flow rates, where E is Young's modulus, mu the modulus of rigidity, r the radius of the helix, and d the helical pitch. Experiments were carried out to determine the above quantity for Salmonella flagellar filaments assuming a close-coil form. Because the above quantity is almost equal to 2 mu for a helical form with a large radius/pitch ratio, we were able to determine the modulus of rigidity for this kind of flagellar filament from plots of elongation vs. flow rates. The modulus of rigidity was determined to be about 1 X 10(11) dyn/cm2, i.e., 2 orders of magnitude larger than the previously estimated value.

Ion transport and its regulation in the endolymphatic sac (ES) are reviewed on the basis of recent lines of evidence. The morphological and physiological findings demonstrate that epithelial cells in the intermediate portion of the ES are more functional in ion transport than those in the other portions. Several ion channels, ion transporters, ion exchangers, and so on have been reported to be present in epithelial cells of ES intermediate portion. An imaging study has shown that mitochondria-rich cells in the ES intermediate portion have a higher activity of Na+, K+-ATPase and a higher Na+ permeability than other type of cells, implying that molecules related to Na+ transport, such as epithelial sodium channel (ENaC), Na+–K+–2Cl− cotransporter 2 (NKCC2) and thiazide-sensitive Na+–Cl− cotransporter (NCC), may be present in mitochondria-rich cells. Accumulated lines of evidence suggests that Na+ transport is most important in the ES, and that mitochondria-rich cells play crucial roles in Na+ transport in the ES. Several lines of evidence support the hypothesis that aldosterone may regulate Na+ transport in ES, resulting in endolymph volume regulation. The presence of molecules related to acid/base transport, such as H+-ATPase, Na+–H+ exchanger (NHE), pendrin (SLC26A4), Cl−–HCO3 − exchanger (SLC4A2), and carbonic anhydrase in ES epithelial cells, suggests that acid/base transport is another important one in the ES. Recent basic and clinical studies suggest that aldosterone may be involved in the effect of salt-reduced diet treatment in Meniere’s disease.