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P Satir

Publications and source records attributed to P Satir.

At least 91 records · Page 5Linked to original sources
PubMed1977

The termination of the central microtubules from the cilia of Tetrahymena pyriformis.

In frayed axonemes of cilia isolated from Tetrahymena pyriformis, observed in negative stain, the central apparatus remains intact, stabilized in part by the sheath projections that encircle the two singlet central microtubules. The projections terminate ca. 1.5 +/- 0.5 micron before the microtubules themselves end. The microtubules are capped together at their tips by a distinct structure, the central pair cap. The cap, ca. 50 nm across and 90 nm long, consists of a stack of two disks and a ball, similar in shape to a finial. The cap is the only part of the axoneme that extends to the distalmost point of the ciliary membrane and, therefore, it may be of significance in length determination or in shaping the ciliary tip.

Animals↗
PubMed1977

Direction of active sliding of microtubules in Tetrahymena cilia.

Axonemes of protozoan (Tetrahymena thermophila BIII) cilia, isolated by the dibucaine method, were treated briefly with trypsin after removal of the ciliary membranes by treatment with Triton X-100. After attachment to polylysine-coated surfaces, the partially digested axonemes remained mainly intact cylinders. Such attached axonemes can be treated with ATP, which induces microtubles sliding. ATP-treated preparations showed disrupted axonemes in which doublets had telescoped out of the original cylinders. These could be captured in place for electron microscopy after critical point drying. Images of this type were used to determine relative movement between adjacent doublet microtubules. Each doublet actively slid relative to its neighbors in a single direction, in which the polarity of force generation of the dynein arms was from base to tip.

Adenosine Triphosphate↗
PubMed1977

Tails of Tetrahymena.

The source of force generation of beating cilia and flagella is an interaction between the doublet microtubules mediated by the dynein-1 arms which cause the doublets to slide relative to one another. Previously, were domonstrated direct sliding of Tetrahymena ciliary axonemes by dark field light microscopy. In this paper, the results of such an experiment have been captured on a polylysine-coated grid surface for whole-mount electron microscopy. Image in which a constant polarity. To produce the observed displacement, the direction of the dynein-1 arm force generation must be from base to tip, so that the doublet (n), to which the arms are attached, pushes the next doublet (n + 1) toward the tip. In addition to the functional polarity, the dynein-1 arms are found to have a structural polarity: they tilt toward the base when viewed along the edges of the A-subfiber. A scheme is presented which reconciles the finding of a single polarity of active sliding with the geometry of microtubule tip displacement of bent cilia.

Adenosine Triphosphate↗
PubMed1976

Splayed Tetrahymena cilia. A system for analyzing sliding and axonemal spoke arrangements.

This study makes use of a procedure designed to illustrate, without serial section analysis, the three-dimensional changes in the ciliary axoneme produced by microtubule sliding, and to confirm essential features of the sliding microtubule hypothesis of ciliary movement. Cilia, isolated from Tetrahymena pyriformis by the dibucaine procedure, are attached to polylysine substratum, and treated with Triton X-100. Critical point drying maintains three-dimensional structure without embedding. The detergent removes the membrane and many axonemes unroll, always in an organized fashion so that doublets follow one another in sequence, according to the enantiomorphic form of the cilium. The central pair of microtubules fall to the side as a unit. The parallel doublet microtubules retain relative longitudinal positions in part by interdoublet or nexin links. Spoke organization and tip patterns are preserved in the opened axonemes. We generalize the work of Warner and Satir (Warner, F. D., and P. Satir, 1976. J. Cell Biol. 63:35-63) to show that spoke group arrangements are maintained for all doublets in straight regions, while systematic displacements occur in bent regions. The conclusion that local contraction of microtubles is absent in the axoneme is strengthened, and direct graphic demonstrations of sliding at the ciliary tip are shown. A morphogenetic numbering scheme is presented which results in a quantitative fit of the tip images to the images predicated by the equation for doublet sliding, and which makes possible new comparisons of structural parameters between axonemes and with cilia of other organisms.

Animals↗
PubMed1975

Ionophore-mediated calcium entry induces mussel gill ciliary arrest.

Lateral cilia of freshwater mussel gills, which normally beat with metachronal rhythm, are arrested pointing frontally by perfusion with 6.25 to 12.5 millimolar calcium and 10(-5) molar A23187, a calcium ionophore. Arrest does not occur in either calcium or ionophore and monovalent cations alone. Activity returns with continued perfusion in potassium chloride or calcium chloride, and more slowly in sodium chloride, after removal of ionophore. These results support the hypothesis that a local rise in internal calcium causes ciliary arrest.

Animals↗
PubMed1975

Laser-induced spreading arrest of Mytilus gill cilia.

Using a "slit camera" recording technique, we have examined the effects of local laser irradiation of cilia of the gill epithelium of Mytilus edulis. The laser produces a lesion which interrupts epithelial integrity. In artificial sea water that contains high K+ or is effectively Ca++ free, metachronism of the lateral cilia continues to either side of the lesion with only minor perturbations in frequency synchronization and wave velocity, such as would be expected if metachronal wave coordination is mechanical. However, in normal sea water and other appropriate ionic conditions (i.e., where Ca++ concentration is elevated), in addition to local damage, the laser induces distinct arrest responses of the lateral cilia. Arrest is not mechanically coordinated, since cilia stop in sequence depending on stroke position as well as distance from the lesion. The velocity of arrest under standard conditions is about 3 mm/s, several orders of magnitude faster than spreading velocities associated with diffusion of materials from the injured region. Two responses can be distinguished on the basis of the kinetics of recovery of the arrested regions. These are (a) a nondecremental response that resembles spontaneous ciliary stoppage in the gills, and (b) a decremental response, where arrest nearer the stimulus point is much longer lasting. The slower recovery is often periodic, with a step size approximating lateral cell length. Arrest responses with altered kinetics also occur in laterofrontal cilia. The responses of Mytilus lateral cilia resemble the spreading ciliary arrest seen in Elliptio and arrest induced by electrical and other stimuli, and the decremental response may depend upon electrotonic spread of potential change produced at the stimulus site. If this were coupled to transient changes in Ca++ permeability of the cell membrane, a local rise in Ca++ concentration might inhibit ciliary beat at a sensitive point in the stroke cycle to produce the observed arrest.

Animals↗
PubMed1974

How cilia move.

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Adenosine Triphosphate↗
PubMed1974

Particle movements in chloroplast membranes: quantitative measurements of membrane fluidity by the freeze-fracture technique.

Stacked chloroplast membranes isolated from Chlamydomonas reinhardtii have differentiated particle arrays when examined by freeze-fracture electron microscopy. When the membranes are isolated unstacked, these particle arrays are lost and the fracture faces have a homogeneous appearance. The changes in appearance are due to rearrangement of existing membrane components by lateral particle movements in the plane of the fluid chloroplast membranes, since quantitative measurements demonstrate almost complete conservation of numbers and sizes of membrane particles during experimentally controlled stacking and unstacking.

Chlamydomonas↗
PubMed1974

The structural basis of ciliary bend formation. Radial spoke positional changes accompanying microtubule sliding.

The sliding microtubule model of ciliary motility predicts that cumulative local displacement (Deltal) of doublet microtubules relative to one another occurs only in bent regions of the axoneme. We have now tested this prediction by using the radial spokes which join the A subfiber of each doublet to the central sheath as markers of microtubule alignment to measure sliding displacements directly. Gill cilia from the mussel Elliptio complanatus have radial spokes lying in groups of three which repeat at 860 A along the A subfiber. The spokes are aligned with the two rows of projections along each of the central microtubules that form the central sheath. The projections repeat at 143 A and form a vernier with the radial spokes in the precise ratio of 6 projection repeats to 1 spoke group repeat. In straight regions of the axoneme, either proximal or distal to a bend, the relative position of spoke groups between any two doublets remains constant for the length of that region. However, in bent regions, the position of spoke groups changes systematically so that Deltal (doublet 1 vs. 5) can be seen to accumulate at a maximum of 122 A per successive 860-A spoke repeat. Local contraction of microtubules is absent. In straight regions of the axoneme, the radial spokes lie in either of two basic configurations: (a) the parallel configuration where spokes 1-3 of each group are normal (90 degrees ) to subfiber A, and (b) the tilted spoke 3 configuration where spoke 3 forms an angle (theta) of 9-20 degrees . Since considerable sliding of doublets relative to the central sheath ( approximately 650 A) has usually occurred in these regions, the spokes must be considered, functionally, as detached from the sheath projections. In bent regions of the axoneme, two additional spoke configurations occur where all three spokes of each group are tilted to a maximum of +/- 33 degrees from normal. Since the spoke angles do not lie on radii through the center of bend curvature, and Deltal accumulates in the bend, the spokes must be considered as attached to the sheath when bending occurs. The observed radial spoke configurations strongly imply that there is a precise cycle of spoke detachment-reattachment to the central sheath which we conclude forms the main part of the mechanism converting active interdoublet sliding into local bending.

Animals↗
PubMed1973

Membrane fusion in a model system. Mucocyst secretion in Tetrahymena.

The freeze-fracture, freeze-etch technique can be employed to reveal new details of the process of fusion of two unit membranes For this study, mucocyst discharge in Tetrahymena pyriformis provides a model system with certain general implications The undischarged mature mucocyst is a saclike, membrane-bound, secretory vesicle containing crystalline material The organelle tip finds its way toward a special site, a rosette of 150 A diameter particles within the plasma membrane. To match this site, the mucocyst membrane forms an annulus of 110 A diameter particles, above whose inner edge the rosette particles sit. Discharge of some mucocysts is triggered by fixation. As discharge proceeds, the organelle becomes spherical and its content changes from crystalline to amorphous. The cytoplasm between the two matching membrane sites is squeezed away and the membranes fuse Steps in membrane reorganization can be reconstructed from changes in rosette appearance in the fracture faces. First, a depression in the rosette-the fusion pocket-forms. The rosette particles spread at the lip as the pocket deepens and enlarges from 60 to 200 nm. The annulus particles then become visible at the lip, indicating completed fusion of the A fracture faces of mucocyst and plasma membranes The remaining B faces of the two membranes have opposite polarities When the content of the mucocyst is released, the edges of these faces join so that the unit membrane runs uninterruptedly around the lip and into the pocket.

Animals↗