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P Satir

Publications and source records attributed to P Satir.

At least 73 records · Page 4Linked to original sources
PubMed1981

The mechanochemical cycle of the dynein arm.

A dynein arm attachment cycle produces sliding between adjacent doublet microtubules (N and N + 1) of cilia. In intact axonemes, in the absence of ATP, almost all arms appear attached at both ends (rigor). When ATP is added, most arms detach from doublet N + 1. In ATP and vanadate, the arms do not return to rigor, suggesting that ATP hydrolysis is required for re-extension and reattachment of the dynein arm, but not for detachment. Using solutions containing dynein to decorate dynein-less axonemal doublets, we confirm this interpretation. In the absence of ATP, both sides of each doublet decorate with arms. Addition of ATP, ATP and vanadate or AMP-PNP causes immediate arm detachment, but only in the first instance, where extensive ATP hydrolysis can occur, does decoration eventually reappear. Dynein decorates heterologous axonemal doublets and brain microtubules, as well as homologous doublets, suggesting that this mechanochemical cycle may have general applicability in microtubule-based cell motility.

Adenosine Triphosphatases↗
PubMed1981

Septate junction disruption and surface reorganization by non-lethal Ca2+ shock.

Using potassium pyroantimonate as a Ca2+ chelating agent, we have been able to open the belt desmosome that mechanically couples adjacent ciliated lateral (L) gill epithelial cells of freshwater mussels. Subsequent transfer of the mechanically uncoupled epithelia to solutions containing millimolar Ca2+ results in dramatic alterations in cell shape and partial disruption and apical reorientation of L cell septate junction. The calls remain viable throughout the procedure as determined by the persistence of ciliary activity, although disruption is accompanied by a separation of neighboring groups of cilia and a switch from metachronal to synchronous L cell ciliary beat co-ordination.

Animals↗
PubMed1981

5-hydroxytryptamine-stimulated mitochondrial movement and microvillar growth in the lower malpighian tubule of the insect, Rhodnius prolixus.

Rapid initiation of ion transport occurs in the lower Malpighian tubule of the insect Rhodnius prolixus following feeding in vivo or stimulation with 5-hydroxytryptamine (5-HT) in vitro. Using the electron microscope, we have conducted a morphometric analysis of cells in the lowest one-third of the lower tubule, demonstrating that 5-HT also induces mitochondrial movement and microvillar growth simultaneously with, but independent of, the onset of ion transport. Mitochondria move from a position below the cell cortex to one inside the microvilli within 10 min of stimulation with 5-HT, resulting in an 8- to 10-fold increase in the volume of mitochondria within the microvilli. Previous findings indicated that mitochondrial movement is dependent on actin-containing microfilaments, but not microtubules. As the mitochondria enter the microvillus, the core microfilaments are reorganized into a sheath of microfilaments, which extends closely parallel to the outer mitochondrial membrane down into the cell interior. This sheath of microfilaments is also observed around mitochondria in the axopods. We suggest that the core microfilaments are responsible for mitochondrial movement into the microvilli and axopods. Stimulation with 5-HT induces a shift in mitochondrial configuration from orthodox to condensed, indicating a possible increase in oxidative phosphorylation. Following stimulation, the microvilli grow about 3 X in volume and 2.5 X in surface area. These increases are more than can be accounted for by mitochondrial invasion and must involve the addition of new membrane and microfilament polymerization. The observed changes - microvillar growth, insertion of additional membrane, activation and movement of mitochondria adjacent to the ion transport membrane - are described in the light of their significance in ion transport. A simple model is proposed which unifies the observed ultrastructural changes and known ion movements in the lower tubule.

Animals↗
PubMed1980

Role of coated vesicles, microfilaments, and calmodulin in receptor-mediated endocytosis by cultured B lymphoblastoid cells.

Cell surface receptor IgM molecules of cultured human lymlphoblastoid cells (WiL2) patch and redistribute into a cap over the Golgi region of the cell after treatment with multivalent anti-IgM antibodies. During and after the redistribution, ligand-receptor clusters are endocytosed into coated pits and coated vesicles. Morphometric analysis of the distribution of ferritin-labeled ligand at EM resolution reveals the following sequence of events in the endocytosis of cell surface IgM: (a) binding of the multivalent ligand in a diffuse cell surface distribution, (b) clustering of the ligand-receptor complexes, (c) recruitment of clathrin coats to the cytoplasmic surface of the cell membrane opposite ligand-receptor clusters, (d) assembly and (e) internalization of coated vesicles, and (f) delivery of label into a large vesicular compartment, presumably partly lysosomal. Most of the labeled ligand enters this pathway. The recruitment of clathrin coats to the membrane opposite ligand-receptor clusters is sensitive to the calmodulin-directed drug Stelazine (trifluoperazine dihydrochloride). In addition, Stelazine inhibits an alternate pathway of endocytosis that does not involve coated vesicle formation. The actin-directed drug dihydrocytochalasin B has no effect on the recruitment of clathrin to the ligand-receptor clusters and the formation of coated pits and little effect on the alternate pathway, but this drug does interfere with subsequent coated vesicle formation and it inhibits capping. Cortical microfilaments that decorate with heavy meromyosin with constant polarity are observed in association with the coated regions of the plasma membrane and with coated vesicles. SDS-polyacrylamide gel electrophoresis analysis of a coated vesicle preparation isolated from WiL2 cells demonstrates that the major polypeptides in the fraction are a 175-kdalton component that comigrates with calf brain clathrin, a 42-kdalton component that comigrates with rabbit muscle actin and a 18.5-kdalton minor component that comigrates with calmodulin as well as 110-, 70-, 55-, 36-, 30-, and 17-kdalton components. These results clarify the pathways of endocytosis in this cell and suggest functional roles for calmodulin, especially in the formation of clathrin-coated pits, and for actin microfilaments in coated vesicle formation and in capping.

B-Lymphocytes↗
PubMed1980

Structural basis of ciliary movement.

All motile somatic cilia, including those of the human respiratory tract, are similar in ultrastructure in that they consist of an axenome of 9 + 2 microtubules surrounded by a specialized extension of the cell membrane. The axonemal elements provide the ciliary motor, which is powered by ATP hydrolysis. In respiratory cilia, mutants occur where axonemal assembly is aberrant such that the doublet attachments known as arms (Afzelius and co-workers) or spokes (Sturgess) have been shown to be missing. These mutant cilia are apparently nonmotile. In model cilia, the arms are composed of dynein, a class of ATPase isoenzymes and associated polypeptides characterized byGibbons and colleagues. In negative stain preparations of arms, three subunits can be seen. In the presence of ATP, dynein functions with a set polarity to form transient cross-bridges that cause the microtubule doublets of the axoneme to slide relative to one another. After brief trypsin treatment, the axonemal microtubules slide almost completely apart with the arms of doublet n pushing doublet n + 1 in a tipward direction. To produce ciliary beating in vivo, sliding is carefully controlled and coordinated, in part probably by the spoke system. The ciliary membrane is responsible for maintaining the appropriate levels of ATP, Mg2+, and Ca2+, and Ca2+ (ca. 10(-7) M) around the axoneme. The beat of certain cilia--e.g., L cilia of mussel gills--can be arrested by increasing axonemal Ca2+ concentration, for example, in the presence of the ionophore A23187 and high external Ca2+. Although the net results of changes in axonemal Ca2+ concentration are not always complete stoppage of beat or of sliding, this ion is also part of the general behavioral control of ciliary motility.

Adenosine Triphosphate↗
PubMed1979

Effect of vanadate on gill cilia: switching mechanism in ciliary beat.

Lateral (L) cilia of freshwater mussel (Margaritana margaritifera and Elliptio complanatus) gills can be arrested in one of two unique positions. When treated with 12.5 mM CaCl2 and 10(-5) M A23187 they arrest in a "hands up" position, ie, pointing frontally. When treated with approximately 10 mM vanadate (V) they arrest in a "hands down" position, ie, pointing abfrontally. L-cilia treated with 12.5 mM CaCl2 and 1 mM NaN3 also arrest in a "hands down" position; substitution of 20 mM KCl and 1 mM NaN3 causes cilia to move rapidly and simultaneously to a "hands up" position. The observations suggest that there are two switching mechanisms for activation of active sliding in ciliary beat one at the end of the recovery stroke and the other at the end of the effective stroke; the first is inhibited by calcium and the second by vanadate or azide. This is consistent with a model of ciliary beating where microtubule doublet numbers 1, 2, 3, and 4 are active during the effective stroke while microtubule doublets numbers 6, 7, 8, and 9 are passive, and the converse occurs during the recovery stroke.

Animals↗
PubMed1979

Evidence of microfilament-associated mitochondrial movement.

The mitochondria in the lower Malpighian tubule of the insect Rhodnius prolixus can be stimulated by feeding in vivo and by 5-hydroxytryptamine in vitro, to move from a position below the cell cortex to one inside the apical microvilli. During and following their movement into the microvilli, the mitochondria are intimately associated with the microfilaments of the cell cortex and microvillar core bundle. Bridges approximately 14 nm in length and 4 nm in diameter are observed connecting the microvillar microfilaments to the outer mitochondrial membrane and microvillar plasma membrane. Depolymerization of all visible microtubules with colchicine does not inhibit 5-HT-stimulated mitochondrial movement. On the other hand, treatment with cytochalasin B does block mitochondrial movement, suggesting that microfilaments play a role in the mitochondrial motility. We have labeled the microvillar microfilaments, which are 6 nm in diameter, with heavy meromyosin, which supports the contention that they contain actin. A model of the mechanism of mitochondrial movement is presented in which mitochondria slide into position in the microvilli along actin-containing microfilaments in a manner analogous to the sliding actin-myosin model of skeletal muscle.

Animals↗
PubMed1979

Insect axopods.

Using the elctron microscope we have found axopods, a cell organelle previously undescribed in multicellular animals, in the lower Malpighian tubule of the insect. Rhodnius prolixus. The axopods, which are 0.2 to 0.8 micrometer in diameter and 10 or more micrometer in length, derive from the luminal surface of the tubule and contain an array of 1 to about 46 microtubules each. These microtubules arise within the cell near the cell junctions or near clumps of mitochondria. Uric acid crystals which occur naturally in the lower tubule have been observed to move down the tubule under experimental conditions where peristalsis and fluid secretion can be ruled out. We suggest that the axopods are motile and serve to transport the crystals along the narrow tubule lumen. Since cilia are not found on somatic cells of arthropods, we suggest that axopods have evolved in the lower tubule to perform a function analogous to a ciliated epithelium in other animals.

Animals↗
PubMed1979

A sliding microtubule model incorporating axonemal twist and compatible with three-dimensional ciliary bending.

1. Equations are developed to calculate the relative displacements of the doublet microtubules at the tip of a cilium when the microtubules twist about the axis of the organelle. 2. Displacements measured from electron micrographs show asymmetry (or skew) which can be matched quantitatively by the theoretical model with the appropriate selection of twist angle and orientation of the axoneme with respect to the plane of beat. 3. For Elliptio cilia the experimental results are consistent with a planar effective stroke and a recovery stroke involving a three-dimensional bend. The plane of the effective stroke is not normal to a surface containing the central pair of microtubules but contains microtubule 2 to produce the observed skew. 4. This model for the beat also explains the range of orientations of axoneme observed in sections through the metachronal wave.

Animals↗
PubMed1978

Calcium control of ciliary arrest in mussel gill cells.

After several hours in 20 mM sodium phosphate and 40 mM KCI (pH 7.4) or similar simple solutions, ciliated cells exfoliate en masse from stripped gill epithelium of freshwater mussels, e.g., Elliptio complanatus. Three types of ciliated cells--lateral (L), laterofrontal (LF), and frontal (F)--can be distiniguished and counted separately in the suspensions. About one-half of the cells of each type remain motile. Motility is unaffected by addition of 10(-5) M A23187 or 10(-2) M Ca+2 added separately, but when ionophore and Ca+2 are added together, ciliary beat is largely arrested. Treatment of the cells with Triton X-100 (Rohm & Haas Co., Philadelphia, Pa.) results in a total loss of motility as the ciliary membrane becomes disrupted. Such models can be reactivated by addition of ATP and Mg+2. All ciliated cell types are reactivated to about the same extent. At least 80% of the activity of the untreated preparation returns. Ca+2-EGTA buffers added to the reactivating solutions permit titration of free Ca+2 concentration vs. percent motility. Activity is unchanged for all cell types at Ca+2 less than 10(-7) M; at 10(-6) Ca+2, L cilia of all cell types are arrested differentially, whereas at Ca+2 greater than 10(-4) M most cilia of all cell types are arrested. We conclude: (a) that increasing cytoplasmic Ca+2 is directly responsible for ciliary arrest, (b) that the readily reversible physiological arrest response of the L cilia in the intact gill is caused by a rise in free Ca+2 in narrow limits from ca. 5 x 10(-7) M to ca. 8 x 10(-7) M, and (c) that the site which is sensitive to Ca+2 is part of the ciliary axoneme or the basal apparatus.

Adenosine Triphosphate↗