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J McLeese

Publications and source records attributed to J McLeese.

5 recordsLinked to original sources
PubMed1998

Factors influencing the steady-state distribution and exchange of thyroid hormones between red blood cells and plasma of rainbow trout, Oncorhynchus mykiss.

We studied effects of in vitro conditions on the steady-state distribution and exchange of thyroid hormones (TH) between red blood cells (RBC) and plasma of rainbow trout. At steady state at 12 degrees C the RBC contained 5-11% of L-thyroxine (T4), 14-23% of 3,5,3'-triiodo-L-thyronine (T3), and 23-24% of 3,3',5'-triiodo-L-thyronine (rT3) present in whole blood. The steady-state distribution was (i) higher in immature than in mature trout for T3, (ii) increased by incubation temperature from 0 to 22 degrees C for both T4 and T3, (iii) unaltered by blood T4 or T3 concentration (0-40 ng/ml), and (iv) increased by O2 gassing and decreased by N2 gassing for T4 and rT3, but negligibly for T3. The exchange between RBC and plasma was more rapid for T3 (50% of maximal influx or efflux at 30-40 s) than rT3 (14 min) than T4 (30 min). Efflux of T4 and T3 was greatly reduced in the absence of plasma protein. Incubation with 10% bovine serum albumin extracted > 98% of labeled T4 and T3 from RBC. We conclude that for trout (i) steady-state distribution and exchange kinetics between RBC and plasma differ greatly for T4, T3, and rT3 and vary with the in vitro conditions, (ii) almost all TH in RBC are reversibly bound to intracellular sites, (iii) efflux is strongly influenced by plasma binding sites, (iv) T3 exchange is rapid and may allow T3 access to RBC TH receptors, buffer plasma T3 levels, or aid T3 delivery to tissues, (v) T4 exchange is slow and this may prevent oxygenation state from altering T4 uptake into RBC, and (vi) rT3 uptake into RBC may contribute to low rT3 levels in trout plasma.

Animals↗
PubMed1996

Maleate modifies apical endocytosis and permeability of endoplasmic reticulum membranes in kidney tubular cells.

Previous studies have shown that histochemical modifications of the endoplasmic reticulum in epithelial cells might be related to their transport function. We have examined the effect of sodium maleate, which produces generalized transport derangement reminiscent of Fanconi syndrome, on the organization, morphology and enzyme activities of endoplasmic reticulum in rat kidney cells. The osmium impregnation technique has revealed that apical vacuoles increase in volume and in number in most proximal tubule cells, and contain osmium deposits. Osmium impregnation of the endoplasmic reticulum is much reduced. In vitro studies, performed with isolated microsomes, show NADPH cytochrome c reductase activity in both normal and maleate-treated rats. As revealed by vanadate, Ca+-ATPase activity in isolated microsomes is unnaffected by maleate but the vanadate-insensitive or passive component of calcium uptake increases particularly later in the response. Therefore, the remaining calcium uptake in the presence of vanadate is indeed passive; in vivo maleate administration also appears to increase the passive entry of calcium into the microsomal compartment. The morphological and histochemical alterations of the endoplasmic reticulum cisternae occur rapidly and with a similar time course to the transport defects, suggesting that this organelle plays a role in transcellular transport. Maleate may directly affect the endoplasmic reticulum membranes whereby passive permeability to calcium is increased. The endocytotic apparatus and possibly exocytosis phenomena are modified by maleate as shown by the increased vacuolization and the presence of black osmium deposits in vacuoles.

Animals↗
PubMed1990

Morphogenesis of endoplasmic reticulum in Xenopus oocytes after microinjection of rat liver smooth microsomes.

We have determined the kinetics of endoplasmic reticulum (ER) reconstitution following insertion of rat-liver smooth microsomes (SM) into Xenopus oocyte cytoplasm using electron microscopy as well as cytochemistry and thick-section 3-dimensional reconstruction. Oocytes were fixed 0, 10, 20, 40, 80, and 120 min after microinjection with SM and processed for thin- and thick-section electron microscopy. At 0 min postinjection, rat liver SM were observed as small vesicles and were loosely dispersed amongst oocyte organelles. At 10 min, tubules were discerned among many elongate vesicles; and these structures comprised large cytoplasmic regions delimited by mitochondria and yolk platelets. By 20 min, segregation of transplanted organelles yielded yolk-platelet-free regions composed of few vesicles but increasingly numerous, long and anastomosing tubules. By 40 min, a network with numerous tubular branches and fenestrations was observed among the few remaining vesicles. By 80 min, transformation of rat liver SM into a complex network of branching and anastomosing tubules was complete. Three-dimensional reconstruction revealed the network to be composed of interconnecting elements consisting of anastomosing tubules. The reconstituted network of anastomosing tubules in Xenopus oocytes was compared to the network of anastomosing tubules in rat liver hepatocytes and was found to be essentially identical. Network formation occurred in oocytes pretreated with either vinblastine (40 microM) or nocodazole (0.166 microM), and network organization was maintained in oocytes treated with the same drugs after microinjection and reconstitution. We conclude that SM retain sufficient molecular information for rapid self-assembly into structures resembling those in the cells from which they were derived. Both the assembly and maintenance of ER structure in oocyte cytoplasm are microtubule-independent. The formation of such structures following microinjection of SM into living cells provides a unique assay for this type of membrane subfraction.

Animals↗
PubMed1990

Fasting induces modifications of the endoplasmic reticulum in intestinal cells.

The polymorphism of the endoplasmic reticulum (ER) in epithelial cells with different transport functions such as the enterocyte suggests that the ER may be involved in some way in molecular transport. To further access this possibility, we examined the ER from the intestine of winter flounder, Pseudopleuronectes americanus, a species which undergoes an annual fast of approximately 6 months' duration, a time during which previous work indicates nutrient carrier number does not change. Fish from June (feeding) and January (8-10 weeks fasted) were sampled. Tissues from the pyloric caeca, foregut, midgut, and hindgut were prepared for electron microscopy using two techniques of staining. Cell height was unaltered in any section, although microvillar length shortened variably. Cellular organization, including position of nuclei, number and distribution of mitochondria, and presence of basolateral membranes, did not change. The ER appeared equally abundant in June and January. However, use of the osmium impregnation technique, which is specific for ER cisternal contents, revealed a change in the impregnation of ER, from a heavily impregnated network in summer to little or no impregnation in winter. These results suggest that a shift in function of the ER had occurred when nutrient transport ceased, and supports a role of the ER in nutrient transport.

Animals↗