Microtubule dynamics and glutathione metabolism in phagocytizing human polymorphonuclear leukocytes.

Glutathione oxidants such as tertiary butyl hydroperoxide were shown previously to prevent microtubule assembly and cause breakdown of preassembled cytoplasmic microtubules in human polymorphonuclear leukocytes. The objectives of the present study were to determine the temporal relationship between the attachment and ingestion of phagocytic particles and the assembly of microtubules, and simultaneously to quantify the levels of reduced glutathione and products of its oxidation as potential physiological regulators of assembly. Polymorphonuclear leukocytes from human peripheral blood were induced to phagocytize opsonized zymosan at 30 degrees C. Microtubule assembly was assessed in the electron microscope by direct counts of microtubules in thin sections through centrioles. Acid extracts were assayed for reduced glutathione (GSH) and oxidized glutathione (GSSG), by the sensitive enzymatic procedure of Tietze. Washed protein pellets were assayed for free sulfhydryl groups and for mixed protein disulfides with glutathione (protein-SSG) after borohydride splitting of the disulfide bond. Resting cells have few assembled microtubules. Phagocytosis induces a cycle of rapid assembly followed by disassembly. Assembly is initiated by particle contact and is maximal by 3 min of phagocytosis. Disassembly after 5-9 min of phagocytosis is preceded by a slow rise in GSSG and coincides with a rapid rise in protein-SSG. Protein-SSG also increases under conditions in which butyl hydroperoxide inhibits the assembly of microtubules that normally follows binding of concanavalin A to leukocyte cell surface receptors. No evidence for direct involvement of GSH in the induction of assembly was obtained. The formation of protein-SSG, however, emerges as a possible regulatory mechanism for the inhibition of microtubule assembly and induction of their disassembly.

Environmental and Endogenous Factors Influencing Emigration in Juvenile Anadromous Alewives

We analyzed juvenile anadromous alewife migration at Bride Lake, a coastal lake in Connecticut, during summer 2006 and found that migration on 24-hour and seasonal timescales was influenced by conditions of the environment and characteristics of the individual. To identify environmental cues of juvenile migration, we continuously video recorded fish at the lake outflow and employed information-theoretic model selection to identify the best predictors of daily migration rate. More than 80% of the approximately 320,000 juveniles that migrated from mid-June to mid-August departed in three pulses lasting one or two days. Pulses of migration were associated with precipitation events, transient decreases in water temperature and transient increases in stream discharge. Diel timing of migration shifted over the summer. Early in the season most migration occurred around dawn; late in the season migration occurred at night. To identify individual characteristics associated with migratory behavior, we compared migrating juveniles that we collected as they were exiting Bride Lake to non-migrating juveniles that we collected from the center of the lake. Migrants were a non-random subset of the population; they were on average 1 – 12 mm larger, 2 – 14 d older, had grown more rapidly (11% greater length-at-age), and were in better condition (14% greater mass-at-length) than non-migrant fish. We infer that the amount of accumulated energy has a positive effect on the net benefit of migration at any time in the migratory season.