Messages are received both near and far, they show, to create transient and sustained responses. The cone presynaptic terminal is highly invaginated, with ribbons of glutamate-containing vesicles above each invagination. Cones respond to changes in light with graded changes in membrane potential. Decreases in light intensity depolarize cones and increase glutamate release, which then activates a class of cells known as Off bipolar cells. In the new report, DeVries et al. show that Off bipolar cell dendrites contact cone terminals at two sites. Most subtypes of Off bipolar cells contact the base of the cone terminal, 300 nm away from the vesicle fusion sites. The group found, however, that one Off cell subtype extended its dendrites up into each invagination to end close to fusion sites. These contacts within invaginations experienced large, rapid fl uctuations in glutamate levels when a cone was depolarized. Glutamate then spilled out of the invaginations to the basal contacts. In spite of their distance from release sites, even a single vesicle's worth of glutamate was able to reach and activate these cells. Distance exacted a toll, however, as the glutamate concentrations sensed by these cells fl uctuated more slowly and at much lower levels. The invaginating cell senses glutamate via AMPA receptors, which recover rapidly from glutamate-induced desensitization and can thus decode rapid consecutive pulses. Basal cells instead use kainate receptors, which have much slower recovery times and produce responses that average over rapid fl uctuations in glutamate concentration. The basally located Off bipolar cells thus generate more sustained responses. The steady signal conveys the basic sight information of change magnitude and duration. The transient signal saying just that there was a change "is probably very important," says DeVries, "because it can help an animal avoid predators or moving objects."

Successful immune defense requires integration of multiple effector systems to match the diverse virulence properties that members of the microbial world might express as they initiate and promote infection. Human neutrophils--the first cellular responders to invading microbes--exert most of their antimicrobial activity in phagosomes, specialized membrane-bound intracellular compartments formed by ingestion of microorganisms. The toxins generated de novo by the phagocyte NADPH oxidase and delivered by fusion of neutrophil granules with nascent phagosomes create conditions that kill and degrade ingested microbes. Antimicrobial activity reflects multiple and complex synergies among the phagosomal contents, and optimal action relies on oxidants generated in the presence of MPO. The absence of life-threatening infectious complications in individuals with MPO deficiency is frequently offered as evidence that the MPO oxidant system is ancillary rather than essential for neutrophil-mediated antimicrobial activity. However, that argument fails to consider observations from humans and KO mice that demonstrate that microbial killing by MPO-deficient cells is less efficient than that of normal neutrophils. We present evidence in support of MPO as a major arm of oxidative killing by neutrophils and propose that the essential contribution of MPO to normal innate host defense is manifest only when exposure to pathogens overwhelms the capacity of other host defense mechanisms.

Extracellular superoxide was detected in cultures of monkey and human arterial smooth muscle cells as indicated by superoxide dismutase inhibitable reduction of cytochrome c. Superoxide production by these cells in the presence of Fe or Cu resulted in modification of low density lipoprotein (LDL). The degree of LDL modification was directly proportional to the rate of superoxide production by cells. Superoxide dismutase (100 &g/ ml), and the general free radical scavengers butylated hydroxytoluene and butylated hydroxyanisole (50 p&M), inhibited Feand Cu-mediated modification of LDL by monkey smooth muscle cells, while catalase (100 pg/ml) and mannitol (25 mM) had no effect.

Two of the cytosolic NADPH oxidase components, p47-phox and p67-phox, translocate to the plasma membrane in normal neutrophils stimulated with phorbol myristate acetate (PMA). We have now studied the translocation process in neutrophils of patients with chronic granulomatous disease (CGD), an inherited syndrome in which the oxidase system fails to produce superoxide due to lesions affecting any one of its four known components: the gp9l-phox and p22-phox subunits of cytochrome b5m (the membrane-bound terminal electron transporter of the oxidase), p47-phox, and p67-phox. In contrast to normal cells, neither p47-phox nor p67-phox translocated to the membrane in PMA-stimulated CGD neutrophils which lack cytochrome b5!m. In one patient with a rare X-linked form of CGD caused by a Pro --His substitution in gp9l-phox, but whose neutrophils have normal levels of this mutant cytochrome bm, translocation was normal. In two patients with p47-phox deficiency, p67-phox failed to translocate, whereas p47-phox was detected in the particulate fraction of PMAstimulated neutrophils from two patients deficient in p67-phox.Our data suggest that cytochrome b5!4 or a closely linked factor provides an essential membrane docking site for the cytosolic oxidase components and that it is p47-phox that mediates the assembly of these components on the membrane. (J. Clin. Invest. 1991. 87:352-356.)