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J Willemot

Publications and source records attributed to J Willemot.

17 recordsLinked to original sources
PubMed1978

Actin- and myosin-like filaments in rat brain pericytes.

Heavy meromyosin (HMM) labeling was used to identify the nature of the filaments which form bundles in the cytoplasm of the pericytes in brain tissue. Rat brain tissue pieces were incubated in glycerol solutions at 4 degrees and then transferred into buffer (pH 7.0), (1) without HMM, (2) with HMM, (3) with HMM + 5 mM ATP, and (4) with HMM + 2.5 mM Na+ pyrophosphate. In pericytes from untreated tissue, smooth-surfaced microfilaments, averaging 6 nm in diameter, appear to branch and anastomose and to anchor on the plasma membrane. After exposure to HMM, the number and the density of the microfilaments are strikingly increased. These tightly-packed microfilaments are now heavily coated with exogeneous HMM thus increasing in width to 18-20 mm. They intertwine in closely-woven networks. After incubation in HMM solutions containing ATP or Na+ phosphate, they are no longer coated with thick sidearms. It can thus be concluded that these microfilaments are of actin-like nature. In addition, after incubation in ATP, they are intermingled with, and converge onto the surfaces of, thick, tapered filaments, which we have tentatively identified as of myosin-like nature. Thus, it appears that certain of the major elements necessary for contraction are present in brain pericytes.

Actins↗
PubMed1975

An ultrastructural study of the microfilaments in rat brain by means of heavy meromyosin labeling. I. The perikaryon, the dendrites and the axon.

Nervous tissue pieces from the caudate nucleus and the substantia nigra of the rat were incubated in cold glycerol solutions of decreasing concentrations and then transferred into standard phosphate buffer (pH 7.0) or into tris-K+-Mg++-Ca++ buffer (pH 7.9) containing HMM, prepared from rabbit skeletal muscle by tryptic digestion. As controls, pieces were immersed for an identical period in the same buffers (1) without HMM or (2) with HMM to which had been added 2.5 mM Na+ pyrophosphate or 5 mM ATP. In control neurons smooth-surfaced microfilaments, about 50 A in diameter, were observed. After reaction with HMM, the microfilaments were increased in number and density and in width to 180-200 A. A meshwork was formed. Arrowheads pointing in the same direction were spaced at regular intervals (300-350 A) among short segments of the surfaces of the microfilaments, depending upon the plane of section. More often, however, typical arrowheads were not observed, and the surfaces of the microfilaments were seen coated with polarized side-arms cross-bridging the spaces between adjacent elements at more or less regular intervals. When cross-sectioned, the microfilaments appeared as dense dots from which a material of lesser electron density radiated. Following incubation in HMM solutions containing Na+ pyrophosphate or ATP, no arrowhead structures were seen. Of particular interest was the structural relation of the actin-like filaments with occasional, tapered myosin-like filaments, and with the plasma membrane, which served as anchor points. Mitochondria and smooth ER membranes were observed to be attached to the actin-like filaments or enmeshed in the network. The microtubules, as well as most of the neurofilaments, were disrupted by the glycerination procedure at 4 degrees, and thus no precision about the structural relationship of the actin-like filaments with the latter elements could be added. The role of the actin-like filaments in the transport of material, by a mechanism of chemomechanical transduction, throughout the neuron from sites of synthesis to functional locations, and between several functional locations, is discussed.

Actins↗
PubMed1975

An ultrastructural study of the microfilaments in rat brain by means of E-PTA staining and heavy meromyosin labeling. II. The synapses.

To identify structures involved in the translocation of the synaptic vesicles towards the presynaptic membrane, an ultrastructural study has been undertaken by means of (1) the E-PTA stain and (2) the HMM-labeling procedure. Using serial sections of E-PTA stained nervous tissue, especially those made in transversal and tangential planes, the geometric order of the presynaptic grid and of its constituents has been described in detail. It consisted of dense projections having the shape of small truncated pyramids cut parallel to their hexagonal bases which rested on the electron-lucent presynaptic membrane. The dense projections were arranged at the points of equilateral triangles. Around each dense projection, six asymmetric hexagonal holes were seen to be arrayed in an hexagonal pattern, forming thus the presynaptic sieve. From the spiny tops of the dense projections, which appeared as specialized structures of the dense material coating the inner surface of the plasma membrane at the level of the synaptic cleft, fine filaments, 40--60 A in diameter, radiated and formed a three-dimensional meshwork pervading the presynaptic bag. The dense cytoplasmic coating delineating the plasma membrane served as anchor points for these microfilaments. Upon incubation with rabbit skeletal muscle HMM the microfilaments underwent specific structural changes, consisting of: (1) a striking increase in diameter; (2) the association of periodic and polarized substructures with their surfaces. The synaptic vesicles and mitochondria were seen to be attached to the numerous HMM-decorated filaments or enmeshed in the network formed by these filaments. The actin-like filaments were anchored to the plasma membrane at many points and to the presynaptic dense projections. Following incubation in the buffer alone or in buffer HMM solutions containing Na+ pyrophosphate or ATP, no arrowheaded structures were observed. Thus, a network consisting of actin-like filaments was demonstrated in the presynaptic bag. Of particular interest was the structural relation of the actin-like filaments with the occasional, tapered myosin-like filaments. The role of the presynaptic actin-like network in the transport of synaptic vesicles towards the presynaptic membrane by a mechanism of chemomechanical transduction is discussed. In the postsynaptic dendrite or dendritic spine, a filamentous network was observed to be attached to the subsynaptic web by means of the E-PTA stain and of the HMM-labeling procedure. The occurrence of an actin-like meshwork in the postsynaptic region is suggested to produce changes in the macromolecular configuration of the postsynaptic membrane by a "mechanoenzyme" system similar to that described in the mitochondrial membrane.

Actins↗
PubMed1975

Studies on protein metabolism during isoproterenol-induced cardiac hypertrophy.

Chronic treatment with isoproterenol (ISO) (30 mug/100 g body wt/day for 21 days) causes a hypertrophy of the heart (approximately 40%). Protein determination made on homogenates of the heart show similar percentages of protein in the control and treated animals. Thus, ISO presumably stimulates protein synthesis in the heart, as its total protein content is increased by chronic treatment. Studies of the stimulation of protein synthesis during a 9-day treatment with ISO have been carried out by following the incorporation of 14C-labeled amino acids in vivo into heart protein. This stimulation attained a maximum after 5 days of treatment and then declined. In other experiments, groups of rats received a single injection of ISO and were killed at various times (from 0 to 48 hr) after the injection. Stimulation of protein synthesis was maximal 3 hr after the injection, and it slowly decreased until the 36th hr. After that time the rate of protein synthesis was equal to that of control animals. Other groups of rats received daily injections of ISO for 9 days and were killed at various times after the ninth injection. Protein synthesis was still stimulated by ISO; however, the stimulation was observed only during the first 12 hr following the injection of the 9th day. There was an apparent inhibition of protein synthesis which lasted from the 30th to the 48th hr following the ninth injection. The rate of protein degradation did not seem to be affected by a chronic treatment with ISO. Thus, the increased rate of protein synthesis seems to be the sole factor responsible for the increase of the total protein content of the heart, even if the stimulation of the incorporation of labeled amino acids decreased after a few days of treatment.

Animals↗