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Biomedical subjects

M Henkart

Publications and source records attributed to M Henkart.

10 recordsLinked to original sources
PubMed1987

Inhibition of NK and ADCC activity by antibodies against purified cytoplasmic granules from rat LGL tumors.

Highly purified preparations of cytoplasmic granules from transplantable rat large granular lymphocyte (LGL) tumor lines (rat natural killer (RNK) tumors) were used to immunize rabbits. Antibodies from these animals gave two precipitin lines with granule extracts in Ouchterlony experiments. They reacted with at least four different bands on nitrocellulose blots of SDS gels of LGL granule proteins. By immunofluorescence, specifically adsorbed antigranule antibodies did not recognize LGL or T cell surface antigens but reacted with the cytoplasmic granules in permeabilized RNK tumor cells as well as with normal rat LGL. These same antisera showed little or no reactivity with a panel of other cells, including peripheral blood T cells, thymocytes, macrophages, and EL-4 tumor cells. F(ab')2 preparations of these antigranule antibodies completely blocked granule-mediated lysis of both SRBC and nucleated targets, while control F(ab')2 preparations from rabbits immunized with EL-4 granules or TNP-KLH showed no significant inhibition of this cytolytic activity at the same antibody concentration. Anti-granule F(ab')2 preparations specifically inhibited (greater than 75%) rat natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) activities in a dose-dependent manner but did not effect cytotoxic T cell activity. Pretreatment of either effectors or targets by these antibodies had no effect. Anti-granule F(ab')2 preparations, at concentrations showing strong inhibition of lysis, did not inhibit the binding of LGL to YAC-1 or Ab-coated P815 targets. These results demonstrate that a granule component(s) is necessary for the lytic activity of LGL in both NK and ADCC and provide the first direct evidence that a secretory event involving these granules is part of the lytic process.

Animals↗
PubMed1987

Secretory processes in lymphocyte function.

The secretion of immunoglobulin by plasma cells has been considered a classical example of the "non-regulated" pathway of protein secretion, in which newly synthesized protein is processed by the Golgi, packaged into small vesicles, and immediately secreted without intracellular storage. In the case of lymphokine secretion by T lymphocytes, it is generally not clear whether this non-regulated pathway is also being used, as opposed to the "regulated" pathway which has been proposed to operate in the cytotoxic lymphocyte mechanism. In this case, as in mast cells and endocrine cells, proteins are synthesized and then stored in cytoplasmic granules. The secretion is triggered (regulated) by a membrane receptor-ligand interaction, which for the cytotoxic lymphocytes is part of the target cell binding process. In cytotoxic T lymphocytes, this secretion process can be measured by following the appearance of a granule serine protease in the medium, and it has been shown to be triggered by target cells or by immobilized antibodies which bind the T cell receptor complex. In addition to cytotoxic lymphocytes, cloned T helper cells contain this serine protease in cytoplasmic granules with a low internal pH. Helper lymphocytes secrete this enzyme in response to (1) soluble antigen which has been processed by cells bearing the appropriate MHC antigens; (2) immobilized antibodies against the T cell receptor complex; (3) a combination of phorbol ester and calcium ionophore. Thus in both helper and cytotoxic lymphocytes, the regulated pathway of protein secretion clearly operates after triggering by the T cell antigen receptor.

Animals↗
PubMed1978

Formation of synapses between cells of a neuroblastoma X glioma hybrid clone and mouse myotubes.

Synapses form between cells of a neuroblastoma X glioma hybrid clone and cultured mouse skeletal myotubes. The synapses are cholinergic, and the acetylcholine release mechanism is dependent on calcium ions. The transmitter output of the synapses is low, with considerable variability in the latency and amplitude of the postsynaptic responses to presynaptic action potentials. The fine structure of physiologically identified functional junctions was examined electron microscopically. Small (50 nm) clear vesicles were seen presynaptically and there were areas with a wide (approx. 50 nm) gap containing basement membrane-like material between the pre- and postsynaptic cells. In addition, in some regions there was a densely staining material lining the muscle membrane and some suggestion of infolding of the muscle membrane. In none of the cases, however, have areas been found where small, clear vesicles cluster around pre- and postsynaptic membrane densities. Thus, functional synapses can occur in the absence of the highly organized synaptic structure seen at mature synapses.

Action Potentials↗
PubMed1977

Mouse spinal cord in cell culture. I. Morphology and intrinsic neuronal electrophysiologic properties.

1. Reliable methods for establishing fetal mouse spinal cord (SC) and dorsal root ganglion (DRG) cells in long term (greater than 1 mo) dissociated cell cultures are described. These cells have been studied by morphologic and intracellular electrophysiologic techniques. 2. Cells studied electrophysiologically can be relocated after preparation for electron microscopy and examined in thin sections. The electron microscope shows that the surface membranes of these cells were directly accessible to the culture medium. The surfaces of SC cells were studded with synaptic boutons, whereas the DRG cell surfaces generally had none. 3. Current-voltage relationships and linear electrotonic properties of the neurons are described. Delayed and anomalous rectification were seen in both cell types. The length of SC cell dendrites was about one characteristic electrotonic length, while little or no contribution of the relatively sparse DRG cell processes was seen in the transient responses of the DRG cells. 4. Postspike and posttetanic hyperpolarizations in DRG cells were due to a surface membrane conductance increase; this was probably primarily an increase in K+ conductance. Post-activation hyperpolarization in SC cells was primarily due to activation of an electrogenic Na+ pump.

Animals↗
PubMed1976

Localization of calcium binding sites associated with the calcium spike in barnacle muscle.

La ion behaves as a competitive inhibitor of Ca ions on the calcium spike in the giant muscle fiber of the barnacle, Balanus nubilus. La-treated muscle fibers, in which the rate of rise of the spike was diminished to a known degree, have been examined with the electron-microscope. In such fibers dense particles are seen in association with the surface membrane and external lamina of the cell. La particles are not seen in association with fibers that have been allowed to recover from La inhibition before fixation. The number of La particles seen in association with the muscle fiber increases with increasing La concentration when the Ca and Mg concentrations are held constant and decreases with increasing Ca and Mg concentration when the La concentration is held constant. The results suggest that the La visible in the electron-microscope under the conditions of these experiments is bound to a class of sites similar to those involved in the Ca spike.

Animals↗
PubMed1976

Similarity of junctions between plasma membranes and endoplasmic reticulum in muscle and neurons.

The structure of membranes at junctions between the plasma membrane and underlying cisterns of endoplasmic reticulum in amphioxus muscle and mouse cerebellar neurons was studied using the freeze-fracture technique. In amphioxus muscle, subsurface cisterns of sarcoplasmic reticulum form junctions with the surface membrane at the level of the sarcomere I bands. On the protoplasmic leaflet of the sarcolemma overlying these junctions were aggregates of large particles. On the protoplasmic leaflet of the membranes of cerebellar basket, stellate and Purkinie cells there were similar aggregates of large particles. In both tissues, the corresponding external membrane halves had arrays of pits apparently complementary to the aggregates of large particles. Cross fractures through junctions showed that the particle aggregates in neuronal and muscle membranes were consistently located over intracellular cisterns closely applied to the plasma membrane. Thus, a similar plasma membrane specialization is found at subsurface cisterns in mammalian neurons and amphioxus muscle. This similarity supports the hypothesis that subsurface cisterns in neurons, like those in muscle, couple some intracellular activity to the electrical activity of the plasma membrane.

Animals↗
PubMed1975

Light-induced changes in the structure of pigmented granules in aplysia neurons.

Pigmented granules in Aplysia neurons prepared in the dark contain material that appears to be composed of 50-angstrom globules and a precipitate, probably a calcium salt. On illumination the globules rearrange into paracrystalline arrays and membrane-like lamellae. The morphologic transformation may be related to calcium release from the granules, and the released calcium may mediate the light-evoked hyperpolarization described by others.

Animals↗
PubMed1975

Computer analysis of organelle translocation in primary neuronal cultures and continuous cell lines.

Organelle translocation in a number of cell types in tissue culture as seen by high-resolution Zeiss-Nomarski differential interference contrast optics was filmed and analyzed by computer. Principal cell types studied included primary chick spinal cord, chick dorsal root ganglion, ratbrain, and various clones of continuous cell lines. Organelle translocations in all cell types studied exhibited frequent, large changes in velocity during any one translocation. The appearance of particles as seen with Nomarski optics was correlated with their fine structures in one dorsal root ganglion neurite by fixing the cell as it was being filmed and obtaining electron micrographs of the region filmed. This revealed the identity of several organelles as well as the presence of abundant neurotubules but no neurofilaments. Primary cell cultures exhibited more high-velocity organelle movements than continuous cell lines. The net progress of an organelle in a given direction was greater in primary neuronal cells than in fibroblasts or continuous cell lines. These findings are correlated with the literature on organelle translocation and axoplasmic transport.

Animals↗