PubMed Health⌕ Search

Biomedical subjects

B Uhrík

Publications and source records attributed to B Uhrík.

34 records · Page 2Linked to original sources
PubMed1984

T-system membranes in microsomal fractions of crayfish muscles: identification and differences in protein composition.

Specific binding of 3H-ouabain and ruthenium red (RR) to membranes of T-tubules in crayfish muscles was used to identify the subfraction containing vesicles originating from the T-system. The microsomal fraction was prepared by differential centrifugation, and subfractions were separated in continuous or discontinuous sucrose density gradients. 3H-ouabain binding was estimated by scintillation counting; RR binding was examined by electron microscopy. The light subfraction was identified using both methods as that containing vesicles of T-tubules. Protein separation by SDS-electrophoresis revealed marked differences between the subfraction containing vesicles of T-tubules and other subfractions, the most distinctive feature being the presence of a protein of Mr 46,000 predominantly in the light subfraction.

Animals↗
PubMed1984

Arrangement and density of junctional feet in crayfish muscle fibres.

Junctional feet in tubulo-reticular junctions of crayfish muscle fibres are arranged tetragonally with a centre-to-centre spacing of 30-34 nm. The resulting density of 860-1110 feet per 1 micron 2 of the junctional membrane is similar to that reported for other animal species. Using data of a previous stereological study, there are 150-190 feet per 1 micron 2 of the total T-tubule surface and 6000-7800 feet per 100 microns 3 of the fibre volume.

Animals↗
PubMed1981

Ultrastructural observations on nodes of Ranvier from isolated single frog peripheral nerve fibres.

A preparative procedure is described by which well-preserved nodes of Ranvier from isolated frog peripheral nerve fibres may be obtained. The following steps are crucial: careful and gentle dissection and isolation of a single nerve fibre, mounting in a chamber limiting lateral movements of the fibre during the fluid exchange, simultaneous glutaraldehyde-OsO4 fixation and embedding in the same chamber used for fixation. Serial sectioning of individual nodes from both motor and sensory fibres made it possible to reconstitute three-dimensional models of several nodes and to study their morphology extensively. In addition to well-known ultrastructural features of the nodal and paranodal architecture, evaginations of a nodal membrane containing mitochondria and outpouchings of the paranodal axoplasm containing vesicles are described.

Animals↗
PubMed1980

A quantitative estimation of components in crayfish muscle fibres by stereological methods.

The volume and surface densities of structural components in isolated long-sarcomere fibres of crayfish (Astacus fluviatilis) were estimated by stereological methods. The relative volumes were as follows (in % of the fibre volume): sarcolemmal invaginations (SI) 0.74; T-system 1.1; whole sarcoplasmic reticulum (SR) 4.7; junctional SR cisternae 0.41; mitochondria 1.1; nuclei 0.57; myofibrils 81.6; peripheral basal lamina 1.1; junctional gap 0.043; lysosomes 0.029. The values for surface densities were (in microns2/100 microns3): peripheral sarcolemma 1.27; SI 7.21; T-system 40.2; whole SR 146.4; junctional SR cisternae 14.88; junctional area of SR cisternae 7.05; mitochondria 8.98; nuclei 0.75; myofibrils 163. The invaginated membranes (SI and T-system) made up 97.4% of the total area of surface membranes and increased the effective area of peripheral sarcolemma 39 times. Using the values of the total electrical capacity from previous investigations on Astacus fibres, the specific capacity of surface membranes was calculated as 1.08 microF/cm2.

Animals↗
PubMed1979

Three-dimensional arrangement of sarcoplasmic reticulum in crayfish as seen by high voltage electron microscope.

Sections several micro thick of single fibres from the crayfish muscle were examined by means of a high voltage electron microscope to find out the geometry of the sarcoplasmic reticulum (SR). A sufficient contrast of the SR was achieved by lead acetate histochemical method for calcium. Longitudinally oriented files of SR vesicles at the level of A bands and interruptions in otherwise continuous SR net are the most conspicuous features.

Animals↗
PubMed1978

Kinetics of functional and morphological changes during decoupling and recoupling induced by glycerol in isolated muscle fibres of the crayfish.

The development of ultrastructural changes in the T-system of isolated muscle fibres of the crayfish by the glycerol procedure is described in correlation with the dissociation of excitation-contraction (E--C) coupling as well as with recoupling of the E--C link. The sequence of events in the process of disconnection of the tubules is as follows: dilation of the T-system tubules, disconnection of the constricted tubular segments from the surface membrane and from the T-system vesicle, disappearance of the lumen and its disintegration. The decoupled state is characterised by the presence of round vesicles uniformly distributed in the entire volume of the fibre. The volume of vesicles accounts well for the residual postglycerol volume increase (15%) of the muscle fibres. Functional and structural recovery can be induced by reapplication of glycerol to fibres decoupled and vesiculated with concentrations of glycerol less than or equal to 300mmol.l(-1) in crayfish saline. The restitution starts with the organisation of the material of the disintegrated connecting segment of the T-system tubule into small vesicles which coalesce to form the tubule from the vesicular site. At the same time the surface membrane is invaginated toward the vesicle, thus forming the tubule from the surface membrane site. Recovery starts already in the first minute after application of glycerol and is completed within approximately 15 min.

Animals↗
PubMed1978

Decoupling of the excitation-contraction link by glycerol procedure in volume-clamped muscle fibers.

The role of "osmotic shock" and vesiculation in the mechanism of disconnection of the T-system tubules by the glycerol procedure was studied in volume-clamped muscle fibres of the crayfish. The transient dilatation of fibres during the wash-out of glycerol was prevented by application of hypertonic sucrose solutions of decreasing osmolarity to hold the fibre volume constant. Under these conditions the fibres were decoupled only partially; the twitch tension was decreased to a steady level of about 40% of the control tension. The decay in tension developed without the transient potentiation observed in fibres allowed to dilate. The decoupling could not be reversed by reapplication of glycerol saline. The structure of volume-clamped fibres differs from the dilated ones in two respects; the vesicles appear smaller and are absent in continuous layers (about 4 micrometer in width) just under the surface and the cleft membranes. Electron microscopy of these regions has revealed the presence of normal T-system tubules communicating with the fibre exterior. The results provide evidence for the secondary role of the osmotic factor and the essential role of the vesiculation in the induction of the detubulation by glycerol procedure.

Animals↗
PubMed1976

Recovery of ultrastructural changes accompanying caffeine contractures in isolated muscle fibres of the crayfish.

Reversible caffeine contractures in isolated muscle fibres of the crayfish (Astacus fluviatilis; m. extensor carpopoditi) are accompanied by swelling of the diadic cisternae of the sarcoplasmic reticulum and by constriction of the T-system tubules. The membranes of the tubules may coalesce and form pentalaminar structures. These changes in the diadic region can be found already in fibres fixed 10 s after the sudden introduction of 4 mM or 6 mM caffeine solution. The changes are completely reversible. The recovery period after a 6 mM caffeine contracture lasts 20 min. The restitution of ultrastructural changes induced by caffeine correlates well with the recovery of responsiveness to a repeated application of caffeine. The pretreatment of fibres with procaine prevents both the generation of caffeine contractures and the occurrence of changes in the ultrastructure. No changes or a very slight enlargement of diadic cisternae were found during potassium contractures of comparable size and duration to caffeine contractures. The effect of procaine as well as the restitution of ultrastructural changes after the recovery of responsiveness to caffeine support the view that the cisternal swelling is a direct consequence of the calcium releasing action of caffeine. Isolated swelling of diadic cisternae and the absence of any changes in the remaining parts of the sarcoplasmic reticulum during reversible caffeine contractures could point to the existence of functional differentiation of the respective parts of the sarcoplasmic reticulum. The absence of ultrastructural changes during potassium contractures might indicate a different source of the activating calcium for contraction and/or a different mechanism of its release.

Animals↗