In five strains of Mycoplasma gallisepticum, a protein with a molecular mass o f about 40 kDa was detected by immunoblotting with anti-pig brain tubulin polyclonal and monoclonal antibodies. In eight other mycoplasma species similarly tested no reaction was observed. T h i n serial sections of M. gallisepticum and Acholeplasma laidlawii cells examined b y transmission electron microscopy revealed a submembrane system of tubules in M. gallisepticum but not in A. laidlawii. The intracellular spatial distribution of the tubular structures was reconstructed. T h i n sections of M. gallisepticum treated with anti-tubulin antibodies and colloidal gold particles (immunogold labelling) revealed distinct labelling of the tubular system. Analysis of the tubular structures b y high resolution electron microscopy and optical diffraction showed their helical organization to be: diameter 40 nm, helix pitch approximately 20 nm and electron-transparent core 10 nm in diameter. A possible involvement of the tubular system in mycoplasma motility is suggested.

In the isolated frog urinary bladder a 20- to 50-fold increase of the osmotic water permeability has been revealed in the absence of arginine vasopressin (AVP) as a result of several successive changes of the serosal Ringer solution. This increase of the osmotic water permeability was of the same magnitude as that of the effect of 1 nM AVP. Similarly to the effect of AVP, the amount of adenosine 3',5'-cyclic monophosphate (cAMP) in the cells rose, and aggregates of intramembraneous particles were formed in the apical plasma membrane of granular cells (as shown by the freeze-fracture method). Immunocytochemical studies using anti-actin monoclonal antibodies indicated depolymerization of F-actin following the AVP-independent change in water permeability. It was possible to decrease the high level of osmotic permeability to the initial level if 10 microl/ml of frog blood serum or a lipid extract of this blood serum, or 1 microM arachidonic acid or 1 nM prostaglandin E2 was added to the serosal Ringer solution. The rapid restoration of the osmotic water impermeability of the epithelium after the AVP- evoked effect was achieved by the addition to the serosal Ringer solution of Ringer solution in which intact frog urinary bladders had been previously incubated for 1 h. The data obtained indicate that the maintenance of the impermeability to water of the osmoregulating epithelium and the restoration of the initial low level of the osmotic permeability after the effect of AVP are due to participation of prostaglandin E2 and other autacoids as well as, probably, some physiologically active substances of a lipid nature that are present in the blood serum.

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A new approach, basing on a resemblance between cytoskeleton structures associated with plasma membranes and interfacial layers of coexisting phases, is proposed. In particular, a lattice model, similar to those of the theory of surface properties of pure liquids and nonelectrolyte solutions (Ono, S., and S. Kondo. 1960. Handbuch der Physik.), has been developed to describe nerve fiber cytoskeleton. The preliminary consideration of the model shows the existence of submembrane cytoskeleton having increased peripheral densities of microtubules (compared with the bulk density) which is in qualitative agreement with the data in literature. Some additional possibilities of the approach proposed are briefly discussed.

Hyaluronidase (30 U/ml) added from the mucosal side of the frog urinary bladder (pH 5.4, 25~ is shown to increase the permeability of its wall for water and to shorten fibrillary structures of the apical glycocalyx. The hyaluronidase-mediated increase in osmotic permeability is smaller, and occurs later, than that produced by arginine vasopressin. Key Words: vasopressin; hyaluronidase; water permeabilitySome 40 years ago, in an article published in the Bulletin of Experimental Biology and Medicine, Ginetsinskii and coauthors reported that hyaluronidase is released by the kidneys [1]. Four years later, Ginetsinskii advanced a hypothesis attributing a role to this enzyme in the mechanism of action of antidiuretic hormone (ADH) [7]. This hypothesis has not gained wide acceptance, in particular because there is no direct evidence to indicate that osmotic resistance is increased by added hyaluronidase. Previous attempts to increase water permeability by adding hyaluronidase from the mucosal side of the amphibian urinary bladder -the main physiological model used to study the mechanism of action of ADHhave been unsuccessful [5,10]. In the present study, an attempt was made to use a new methodological approach to test hyaluronidase for its effect on the osmotic resistance of the amphibian (frog) bladder wall. MATERIALS AND METHODSThe study was conducted on urinary bladders from winter Rana temporaria frogs. Hyaluronidase was added from the mucosal side of the bladder while the serosal side was bathed with Ringer's solution. The measure of bladder wall permeability was a water flow via an osmotic gradient (expressed in #l/minx xcm2). One portion of the bladder served as the control while the other portion was exposed to hyaluronidase (EC 3.2.1.35; Type I-S), 300 U/mg; Sigma) or to arginine vasopressin (Serva). The method used to assess water permeability was similar to that described previously [6] except that the two bladder portions were weighed on an electronic balance (Gosmetr, St. Petersburg) and the results automatically entered into a computer.For electron microscopic examination, each portion of the bladders was placed for 5-10 min in a 2.5% isotonic glutaraldehyde solution in phosphate buffer (pH 7.4), after which the bladders were cut, fixed in the same buffer for 60 min, washed in a buffered isotonic sucrose solution, and transferred to a 1% OsO 4 solution for 60 min, followed by dehydration by asending alcohols in absolute acetone, em-0007-4888/96/0001-0010515.00 r Plenum Publishing Corporation