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Biomedical subjects

R Eckert

Publications and source records attributed to R Eckert.

At least 145 records · Page 8Linked to original sources
PubMed1972

Cilia: activation coupled to mechanical stimulation by calcium influx.

Ciliated epithelial cells in the oviduct of Necturus maculosus were stimulated mechanically by brief dimpling with a microstylus. This treatment produlced a transient depolarization of the membrane, and a transient increase in the frequency of ciliary beating. The increase in frequency of ciliary beating was related to the concentration of extracellular calcium ion, decreasing with reductiotn in calcium. Addition of lanthanum was followed by a decrease in spontaneous ciliary aictivity and a hyperpolarization of the membrane. In the presence of lanthanum, the transietnt depolarization in response to mechanical stimulation had a shorter timte course, and the concomitant increase in ciliary frequency was greatly reduced. It is concluded that calciuml ions enter the cell as a result of mechanical stimulationi of the membrane, and that calcium influx leads to an increase in the frequency of ciliary activity.

Animals↗
PubMed1972

Genetic modification of electric properties in an excitable membrane (paramecium-calcium conductance-electrophysiological measurements-membrane mutant).

A behavioral deficiency produced by a single gene mutation in Paramecium aurelia was traced to impaired electric excitability of the cell membrane. Evidence is presented that the mutant membrane does not exhibit the normal depolarization-activated increase in calcium conductance responsible for regenerative depolarization in the wild type. Other electric properties characteristic of the wild-type membrane remain normal in the mutant.

Alleles↗
PubMed1972

Calcium dependence of ciliary activity in the oviduct of the salamander Necturus.

1. Ciliary activity in the oviduct of the mud puppy Necturus maculosus was monitored by a photometric technique in normal, decalcified, and Triton X-extracted preparations to investigate the regulatory role of calcium ions.2. The frequency of ciliary beating in the isolated tissue ranged from 0 to 12 beats/sec. The frequency in any one group of cells underwent large cyclical variations with periods of 2 min or more.3. Frequency of beating reached a maximum and remained at a plateau upon addition of 1 mM caffeine. Beating temporarily ceased upon removal of the caffeine.4. Ionophoretic injection of calcium ions into an active cell bathed in Ringer solution produced an increased rate of beating. In cells rendered quiescent by prior decalcification with EGTA, injected calcium rapidly restored ciliary activity.5. Epithelia extracted in Triton X-100 were inactive until reactivated by addition of ATP and magnesium ions. The frequency of beating increased between 0.1 and 4.0 mM ATP in 1 mM magnesium, and between 0.2 and 2.5 mM magnesium in 1 mM ATP.6. The frequency of beating in the ATP-reactivated, Triton-extracted tissue was independent of the calcium ion concentration.7. Cells inactivated by decalcification were reactivated by injection of ATP or by extracellular ATP levels as low as 3 x 10(-8)M.8. It is concluded that the frequency of beating depends directly on the concentration of the available energy source, presumably ATP, and that an indirect dependence of beating frequency on calcium concentration in the living tissue results from rate-limiting effects of intracellular calcium on metabolic steps in pathways leading to ATP synthesis.

Adenosine Triphosphate↗
PubMed1970

Passive electrical properties of Paramecium and problems of ciliary coordination.

Potential recordings made simultaneously from opposite ends of the cell indicate that the cytoplasmic compartment of P. caudatum is nearly isopotential. Measured decrements of the spread of steady-state potentials are in essential agreement with calculated decrements for a short cable model of similar dimensions and electrical constants. Action potentials and passively conducted pulses spread at rates of over 100 microm per msec. In contrast, metachronal waves of ciliary beat progress over the cell with velocities below 1 microm per msec. Thus, electrical activity conducted by the plasma membrane cannot account for the metachronism of ciliary beat. The electrical properties of Paramecium are responsible, however, for coordinating the reorientation of cilia (either beating or paralyzed by NiCl(2)) which occurs over the entire cell in response to current passed across the plasma membrane. In response to a depolarization the cilia assume an anteriorly directed orientation ("ciliary reversal" for backward locomotion). The cilia over the anterior half of the organism reverse more strongly and with shorter latency than the cilia of the posterior half. This was true regardless of the location of the polarizing electrode. Since the membrane potential was shown to be essentially uniform between both ends of the cell, the cilia of the anterior and posterior must possess different sensitivities to membrane potential.

Action Potentials↗
PubMed1969

Ciliary orientation: controlled by cell membrane or by intracellular fibrils?

The cirri of the ciliate Euplotes all asslumne the "reversed" orientation whenever the cell is depolarized and the "forward" orientation whenever the cell is hyperpolarized. Potenitial changes arise spontaneolusly or are induced by electrical or mechanical stimuli. The orientation responses of thte cirri are appatently independent of intracellular "neuromotor" fibrils previously assigned a coordinating function, as they persist after the fibrils are transected.

Cell Membrane↗
PubMed1969

Ionic mechanisms controlling behavioral responses of paramecium to mechanical stimulation.

A mechanical stimulus applied to the anterior part of Paramecium causes a transient increase in membrane permeability to calcium. This permits a calcium current to flow into the cell, causing the membrane potential to approach the equilibrium level for calcium. The transient depolarization which results elicits a reversal in the direction of ciliary beat. When the organisms are free-swimming this is seen as the reversed locomotion of Jennings' "avoiding reaction." In contrast, a mechanical stimulus applied to the posterior part results in increased permeability to potassium ions, and hence an outward potassium current. The hyperpolarization which results causes an increase in the frequency of ciliary beat in the normal direction. In free-swimming specimens this is seen as an increase in the velocity of forward locomotion.

Animals↗
PubMed1968

The flash-triggering action potential of the luminescent dinoflagellate Noctiluca.

The action potential which elicits luminescence in Noctiluca is recorded from the flotation vacuole as a transient all-or-none hyperpolarization in response to either local or general application of inward (bath to vacuole) current. Experiments were performed to determine whether the unorthodox polarities of both the stimulus current and the potential response resulted from uncommon bioelectric mechanisms or from special morphological features of this species. The findings all indicate that the action potential belongs to the familiar class of responses which have their origin in voltage- and time-dependent selective increases in membrane permeability, and that morphological factors account for the observed deviations from normal behavior. Both the stimulus and the response have orthodox polarities provided the vacuole is designated as an "external" extracytoplasmic compartment. Differential recording between vacuole and cytoplasm showed that the action potential occurs across the vacuolar membrane, with the cytoplasmic potential, which at rest is negative with respect to the vacuole, overshooting zero and reversing sign to become transiently electropositive. The rising phase of the action potential therefore depends on active current flow through the vacuolar membrane from the vacuole into the cytoplasm. Propagation of the action potential over the subspherical cell from the locus of stimulation is thought to depend largely on the core conductor properties of the thin perivacuolar shell of cytoplasm which is bounded on its inner surface by the excitable membrane and on its outer surface by inexcitable membranes.

Action Potentials↗
PubMed1967

The subcellular origin of bioluminescence in Noctiluca miliaris.

The light emitted by Noctiluca has its origin in 1 to 5 x 10(4) organelles ("microsources") which are scattered throughout the perivacuolar cytoplasm, and which appear to be the elementary functional units of bioluminescence. Microscopical techniques, image intensification, and microphotometry were employed in their investigation. Microsources are fluorescent, strongly phase-retarding, and range widely in diameter below 1.5 microns. The number of quanta emitted in a flash from a microsource ("microflash") is of the order of 10(5) photons. However, microflashes show a wide range of intensities, which are correlated with the size of the organelles from which they arise. Each organelle responds repetitively and with reproducible time course to a succession of invading triggering potentials. Reversible changes in the intensity of the flash emitted by the whole cell ("macroflash") occur because of graduations in intensity of microflashes rather than as a result of changes in the number of responsive organelles. The shape of the flash emitted by individual microsources resembles that of the macroflash except for slightly shorter rise and decay times. It is concluded that the macroflash results from somewhat asynchronous, but otherwise parallel summation of microflashes.

Action Potentials↗
PubMed1966

Subcellular sources of luminescence in Noctiluca.

The perivacuolar cytoplasm of Noctiluca miliaris contains approximately 10(4) microsources of luminescence, with dimensions of 0.5 to 1.5 microns, which exhibit marked fluorescence with ultraviolet excitation. Local invasion by an action potential elicits light emission (microflashes) from these sources with a coupling latency of about 2 milliseconds. Magnitudes of the microflash vary directly with the dimensions of the source. Time courses of the microflash resemble that of the macroflash emitted by the whole cell but have somewhat shorter time constants. The small discrepancy induration between micro- and macroflash can be explained by the 5- to 10-millisecond asynchrony of microsource triggering that results from the conduction time of the action potential. Reversible gradations in amplitude of the macroflash, as from potentiation or fatigue, result from parallel summation of graded changes in microflash intensity. Thus the macroflash gives a reasonably true picture of the subcellular kinetics of luminescence.

Cytoplasm↗
PubMedDate not supplied

Towards better scanning near-field optical microscopy probes--progress and new developments.

Several approaches are described with the aim of producing near-field optical probes with improved properties. Focused ion beam milling allows the fabrication of small apertures in a controlled fashion, resulting in probes with excellent polarization properties and increased transmission. Microfabrication processes are described that allow the production of apertures of 30-50 nm, facilitating the mass-fabrication of apertured tip structures that can be used in a combined force/near-field optical microscope. Finally, possible future developments are outlined.

Journal Article↗