Exocytosis reconstituted from the sea urchin egg is unaffected by calcium pretreatment of granules and plasma membrane.

Micromolar calcium ion concentrations stimulate exocytosis in a reconstituted system made by recombining in the plasma membrane and cortical secretory granules of the sea urchin egg. The isolated cortical granules are unaffected by calcium concentrations up to 1 mM, nor do granule aggregates undergo any mutual fusion at this concentration. Both isolated plasma membrane and cortical granules can be pretreated with 1 mM Ca before reconstitution without affecting the subsequent exocytosis of the reconstituted system in response to micromolar calcium concentrations. On reconstitution, aggregated cortical granules will fuse with one another in response to micromolar calcium provided that one of their number is in contact with the plasma membrane. If exocytosis involves the generation of lipid fusogens, then these results suggest that the calcium-stimulated production of a fusogen can occur only when contiguity exists between cortical granules and plasma membrane. They also suggest that a substance involved in exocytosis can diffuse and cause piggy-back fusion of secretory granules that are in contact with the plasma membrane. Our results are also consistent with a scheme in which calcium ions cause a reversible, allosteric activation of an exocytotic protein.

Thymus-dependent and thymus-independent subpopulations of intestinal intraepithelial lymphocytes: a granular subpopulation of probable bone marrow origin and relationship to mucosal mast cells.

Intraepithelial lymphocytes have been examined histochemically in the small intestines of normal rats and mice and in thymus-deficient animals (B rats and nude mice). It is concluded that these cells are heterogeneous, consisting of at least two subpopulations. One population contains granules, is thymus-independent, and is probably bone-marrow-derived. The other population does not contain granules and appears to be thymus-dependent. It is suggested that the granular cell, which may be a precursor of mucosal mast cells, is more properly a previously unrecognized nonlymphoid leukocyte of bone marrow origin.

[Inability of large granular lymphocytes to recirculate through blood-lymph barriers]. / Nesposobnost' bol'shykh granuliarnykh limfotsitov retsirkulirovat' cherez gematolimfaticheskie bar'ery.

The level of large granular lymphocytes (LGL) has been determined in thoracic lymph duct and peripheral blood of cattle. It has been shown that in contrast to the blood, these cells are present in the lymph in minor quantities. Unlike blood LGL, lymph LGL have smaller granules in cytoplasm. It is concluded that LGL do not recirculate from blood to central lymph.