Biomedical subjects

N L Allbritton

Publications and source records attributed to N L Allbritton.

23 records · Page 2Linked to original sources

PubMed1993

Localized calcium spikes and propagating calcium waves.

Ca2+ signals control or modulate diverse cellular processes such as cell growth, muscle contraction, hormone secretion, and neuronal plasticity. Elevations in intracellular Ca2+ concentrations can be highly localized to micron and submicron domains or propagated as intra- and intercellular waves over distances as large as 1 mm. Localized, subcellular Ca2+ spikes are thought to selectively activate effector systems such as Ca2+ activated chloride currents in pancreatic acinar cells, neurotransmitter release in synaptic nerve terminals, and morphological changes in neural growth cones. In contrast, long-ranged Ca2+ waves synchronize the activities of different cytoplasmic regions of a single cell, such as cortical granule exocytosis after egg fertilization or coordinate the activities of many cells, such as ciliary beating in pulmonary epithelium. The purpose of this review is to delineate the role of Ca2+ in the generation of localized, subcellular Ca2+ spikes and long-ranged intracellular and intercellular Ca2+ waves.

Animals↗

PubMed1992

Range of messenger action of calcium ion and inositol 1,4,5-trisphosphate.

The range of messenger action of a point source of Ca2+ or inositol 1,4,5-trisphosphate (IP3) was determined from measurements of their diffusion coefficients in a cytosolic extract from Xenopus laevis oocytes. The diffusion coefficient (D) of [3H]IP3 injected into an extract was 283 microns 2/s. D for Ca2+ increased from 13 to 65 microns 2/s when the free calcium concentration was raised from about 90 nM to 1 microM. The slow diffusion of Ca2+ in the physiologic concentration range results from its binding to slowly mobile or immobile buffers. The calculated effective ranges of free Ca2+ before it is buffered, buffered Ca2+, and IP3 determined from their diffusion coefficients and lifetimes were 0.1 micron, 5 microns, and 24 microns, respectively. Thus, for a transient point source of messenger in cells smaller than 20 microns, IP3 is a global messenger, whereas Ca2+ acts in restricted domains.

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PubMed1988

Target cell lysis by cytotoxic T lymphocytes that lack detectable hemolytic perforin activity.

When mouse target cells are subjected to cytolytic attack by mouse CTL cell lines that have been cultured for many months in high levels of IL-2, and have abundant perforin-rich secretory granules, they exhibit two prominent changes: 1) rapid and massive increase (greater than 10-fold) in intracellular Ca2+ concentration and 2) fragmentation of DNA into nucleosome-sized fragments. We show here that when the same target cells are subjected to cytolytic attack by perforin-deficient CTL, either human CTL or primary mouse CTL from peritoneal exudates, the same changes are observed, suggesting that perforin-rich and perforin-deficient CTL kill their target cells by similar (if not identical) mechanisms. It is possible that perforin-deficient CTL produce enough perforin to destroy target cells but not enough to be detected by currently available methods.

Animals↗

PubMed1988

Calcium ion concentrations and DNA fragmentation in target cell destruction by murine cloned cytotoxic T lymphocytes.

To investigate the destruction of target cells by murine CTLs, we examined intracellular Ca2+ concentrations ([Ca2+]i) and DNA fragmentation in target cells. Changes in [Ca2+]i were followed by flow cytometry by loading the cells with indo-1, a Ca2+-binding fluorescent dye, and determining the ration of fluorescence intensities at 405 nm (emission maximum for Ca2+-bound dye) over 480 nm (emission maximum for the free dye). Within minutes after interacting with the cytolytic granule fraction that had been isolated from CTLs, [Ca2+]i in target cells was strikingly increased. A pronounced increase in [Ca2+]i was also observed in target cells when they were specifically recognized by intact CTLs. Since ionomycin, a Ca2+ ionophore, caused a similar increase in [Ca2+]i and lysed cells (provided that extracellular Ca2+ was present), it appears that a sustained high level of [Ca2+]i is cytolytic. In contrast with other cells, CTLs, which have been shown to be refractory to granule-mediated lysis and to be poor targets for other CTLs, did not manifest an elevation in [Ca2+]i when they were similarly loaded with indo-1 and treated with isolated granules. The characteristic cleavage of target cell DNA into nucleosome-sized fragments was also induced by isolated granules as well as by valinomycin, a K+ ionophore, but not by ionomycin. The results support the view that lysis of most target cells by cloned CTLs is due primarily to target cell membrane changes that are fundamentally equivalent to the formation of nonspecific ion channels. The resulting large increase in [Ca2+]i is probably responsible for target cell lysis; and changes in intracellular ion concentrations also appear to be responsible for DNA fragmentation, probably by activating endogenous target cell endonucleases.

Animals↗

PubMed1988

A comparison of the cytolytic properties of murine primary CD8+ cytotoxic T lymphocytes and cloned cytotoxic T cell lines.

Lysates of many highly cytolytic murine primary CD8+ cytotoxic T lymphocytes (CTLs) have no detectable hemolytic activity and only traces of serine esterase activity, indicating a striking paucity or absence of the perforin-rich secretory granules that are abundant in the cytoplasm of murine cloned CTL cell lines. Nevertheless, the primary CTLs are almost as resistant to granule-mediated lysis as CTL cell lines. Moreover, target cells that are lysed by all CTLs so far tested, whether primary or cell lines, show similar rapid and marked increases in intracellular calcium and breakdown of DNA into nucleosome-sized fragments. A parsimonious explanation for all of these findings is that primary CTLs, like the CTL cell lines, exercise their cytolytic activity by means of perforin, but the amounts needed are extremely small and below the level of detection by the current relatively insensitive hemolytic assays.

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