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W R LOEWENSTEIN

Publications and source records attributed to W R LOEWENSTEIN.

At least 19 recordsLinked to original sources
PubMed1964

INTERCELLULAR ELECTRICAL COUPLING AT A FORMING MEMBRANE JUNCTION IN A DIVIDING CELL.

Ion communication between the halves (blastomere) of a dividing cell (Asterias forbesi egg), as determined electrically, diminishes progressively during division as a cell membrane junction forms at the plane of cleavage. Virtually all communication is lost towards the end of division by the time the first intercellular space becomes continuous with the exterior. Resting membrane potentials in both cell halves are essentially equal and constant throughout division.

Animals↗
PubMed1964

INTERCELLULAR DIFFUSION.

Fluorescein-sodium, a fluorescent tracer whose molecular weight is 376, diffuses rather freely from the interior of one cell to another in a gland epithelium (Drosophila) but does not diffuse along the intercellular space to the exterior. The permeability of the junctional surfaces of the cell membranes appears to be high, in contrast to the nonjunctional surfaces and intercellular spaces which represent strong diffusion barriers.

Animals↗
PubMed1964

STUDIES ON AN EPITHELIAL (GLAND) CELL JUNCTION. I. MODIFICATIONS OF SURFACE MEMBRANE PERMEABILITY.

Membrane permeability of an epithelial cell junction (Drosophila salivary gland) was examined with intracellular microelectrodes and with fluorescent tracers. In contrast to the non-junctional cell membrane surface, which has a low permeability to ions (10(-4) mho/cm(2)), the junctional membrane surface is highly permeable. In fact, it introduces no substantial restriction to ion flow beyond that in the cytoplasm; the resistance through a chain of cells (150 ohm cm) is only slightly greater than in extruded cytoplasm (100 ohm cm). The diffusion resistance along the intercellular space to the exterior, on the other hand, is very high. Here, there exists an ion barrier of, at least, 10(4) ohm cm(2). As a result, small ions and fluorescein move rather freely from one cell to the next, but do not leak appreciably through the intercellular space to the exterior. The organ here, rather than the single cell, appears to be the unit of ion environment. The possible underlying structural aspects are discussed.

Animals↗
PubMed1964

STUDIES ON AN EPITHELIAL (GLAND) CELL JUNCTION. II. SURFACE STRUCTURE.

The surface structure of a gland epithelium (Drosophila salivary gland), particularly that at the junction between cells, was examined under the electron microscope. The junctional surface, which in the preceding paper was shown to be highly permeable to ions, has the following structural characteristics. About two-thirds of it are profusely infolded; the surface membranes of adjoining cells interdigitate and present desmosomes. The width of the intercellular space varies considerably. The remainder of the junctional surface, the third that abuts on the lumen, is rather straight. Here, the cell membranes are aligned parallel at a distance of 150 A, and interconnected at regular intervals of 100 A. The connecting material has a high electron opacity, and is about as thick as the cell membranes, but, unlike the latter, has no resolvable unit membrane structure. The surface at the cell base, which in the preceding paper was shown to be rather impermeable, is infolded and resembles the infolded junctional region. The luminal surface exhibits microvilli. Critical surface dimensions are given, and the implications of surface structure in intercellular permeability are discussed.

Animals↗
PubMed1963

SEPARATION OF TRANSDUCER AND IMPULSE-GENERATING PROCESSES IN SENSORY RECEPTORS.

New evidence is presented that spike and transducer processes in sensory receptors are independent events; impulse activity in tile crustacean stretch receptor neuron and the mammalian pacinian corpuscle was selectively blocked by a compound (tetrodotoxin) without affecting any of the parameters of the generator potential.

Animals↗
PubMed1963

SOME ELECTRICAL PROPERTIES OF A NUCLEAR MEMBRANE EXAMINED WITH A MICROELECTRODE.

Electrical potential and resistance were measured with microelectrodes in in situ and isolated nuclei of gland cells of Drosophila flavorepleta. The nucleus-cytoplasm boundary was found to be rather impermeable to ion diffusion. It presents a resistance of the order of 1 ohm cm(2) and sustains a "resting" potential, the nucleoplasm being about 15 mv negative with respect to the cytoplasm. Both the resistance and potential appear to be associated with the nuclear membrane: the potential declines to zero and the resistance to a fraction of its original value, when the membrane is perforated experimentally.

Animals↗
PubMed1961

Effects of temperature on the generator and action potentials of a sense organ.

Charge transfer through the receptor membrane of the nonmyelinated ending of Pacinian corpuscles is markedly affected by temperature. The rate of rise and the amplitude of the generator potential in response to a constant mechanical stimulus increase with temperature coefficients of 2.5 and 2.0 respectively. The duration of the falling phase, presumably a purely passive component, and the rise time of the generator potential are but little affected by temperature. The following interpretation is offered: Mechanical stimulation causes the conductance of the receptor membrane to increase and ions to flow along their electrochemical gradients. An energy barrier of about 16,000 cal/mole limits the conductance change. The latter increases, thus, steeply with temperature, causing both the rate of rise and the intensity of the generator current to increase. The membrane of the adjacent Ranvier node behaves in a distinctly different manner. The amplitude of the nodal action potential is little changed over a wide range of temperature, while the durations of its rising and falling phases increase markedly. The electrical threshold of the nodal membrane is rather constant between 40 and 12 degrees C. Below 12 degrees C the threshold rises, and the mechanically elicited generator current fails to meet the threshold requirements of the first node. Cold block of nerve impulse initiation then ensues, although the receptor membrane still continues to produce generator potentials in response to mechanical stimulation.

Action Potentials↗