Concanavalin A induces an intraluminal alkalinization of thymocyte membrane vesicles

Transport of ions in erythrocytes infected by plasmodia

Throughout its erythrocytic cycle the plasmodial parasite modifies the plasma membrane of its host cell. Some changes derive from parasite metabolism. Intraerythrocytic forms use glucose at more than 10-fold normal red cell rates. The H+ accompanying the lactate end-product is exported into the host cell cytoplasm by an electrogenic proton pump in the parasite membrane. This maintains a pH greater than 7.0 in the parasite cytoplasm, but lowers erythrocyte cytoplasmic pH from approximately 7.2 to 6.5. Ca2+ transport across parasite membranes is coupled to the proton pump, possibly a Ca2+/H+ antiporter. The Ca2+, Mg2+-ATPase and Na+,K+-ATPase activities of erythrocyte membranes from schizont-infected erythrocytes have been studied. Under optimal assay conditions (pH = 7.0; [ATP] = 1 mM; +/- calmodulin) membranes from infected cells showed a 30% reduction in Ca2+,Mg2+-ATPase activity but no difference from normal in Na+,K+-ATPase activity. The calmodulin levels of infected cells were depressed by about 30%. The [ATP] in the cytoplasm of infected erythrocytes was only 0.2 mM (as against 1.3 mM in normals) and at this ATP concentration the activities of both ATPases are only 30% of normal. Shifting the pH from 7.0 to 6.5 decreases Na+,K+-ATPase activity by an additional 50% but is without effect on the Ca2+,Mg2+-ATPase. The results provide a partial explanation for the increased Ca2+ permeability and altered Na+/K+ content of plasmodia-infected erythrocytes.

A time-lapse video image intensification analysis of cytoplasmic organelle movements during endosome translocation

Vital fluorescence staining has been used in conjunction with time-lapse video image intensification microscopy to analyze the distribution and movement of endosomes, lysosomes, and mitochondria in cultured rat ovarian granulosa cells. Exposure of 5-d granulosa cell cultures to pyrene-concanavalin A (P-Con A) or 3,3'-dioctadecylindocarbocyanine-labeled low-density lipoprotein (dil-LDL) at 4 degrees C results in the formation of randomly distributed endosomes 10 min after warming to 37 degrees C that exhibit saltatory motion for 20 min. If granulosa cells are labeled at 4 degrees C with both P-Con A and dil-LDL and warmed to 37 degrees C, both ligands are found within the same endosomes which migrate centripetally to the cell center where label accumulates within phase-dense structures by 60 min. The initial endosome saltations occur over short distances (mean distance = 4.6 micron) with a mean velocity of 0.03 micron/s. Endosome saltations then cease and are followed by a gradual centriptal migration of endosomes to the cell center where they accumulate and fuse with phase-dense structures. The second phase of movement involves a continuous, unidirectional migration of endosomes over distances ranging from 5 to 40 micron at a mean velocity of 0.05 micron/s. Lysosomes were simultaneously visualized as acridine orange-staining, phase-dense structures in control cells and cells exposed to fluorescent ligands. In untreated cells, lysosomes are dispersed throughout the cytoplasm and undergo bidirectional saltations covering a mean distance of 8.7 micron with a mean velocity of 0.3 micron/s. Lysosomes redistribute centripetally to the perinuclear region of the cell by saltatory movement within 20 min of exposure to ligand. Mitochondria were visualized with the fluorescent dye rhodamine 123 in granulosa cells labeled with P-Con A and were found to redistribute to the cell center coincident with endosomes. The microtubule-disrupting agent nocodazole was found to inhibit lysosome saltations and all phases of endosome movement. Taxol, a microtubule-stabilizing agent, partially impaired lysosome movement and led to a redistribution of lysosomes into linear aggregates surrounding the nucleus. Taxol was also found to inhibit endosome movement. The data indicate that (a) endosome movement proceeds initially by saltation and later by a nonsaltatory centripetal migration in association with mitochondria, that (b) lysosomes and endosomes undergo a temporally distinct but spatially similar change in cytoplasmic distribution, and that (c) microtubules are required for the directed translocation of endosomes and lysosomes towards the cell center.

Multistation multiparameter flow cytometry: a critical review and rationale

The capacity for fluorescence excitation by beams of different wavelengths at separate points along the sample stream, and the capacity for computer analysis of multiparameter data thus obtained, are now available in flow cytometer/sorter systems from commercial producers. It is now readily apparent to most experienced users of flow cytometers that such multiparameter analysis offers the most convenient solution to the problem of characterizing subpopulations of cells within a mixed population. The use of multiple beams facilitates resolution of fluorescence signals from several probes within or upon a single cell and widens the range of analytical alternatives available to experimenters. This critical review discusses the history of the instrumentation, the parameters now measurable and the probes used for their measurement, and the methods for data analysis. Required sensitivity and precision are discussed, leading to the conclusion that many of the advantages of multistation, multiparameter flow cytometry can be made available in less complex and less costly instruments using less powerful sources and less elaborate computer hardware than are presently incorporated in commercial apparatus.

High intracellular pH accompanies mitotic activity in murine lymphocytes

Intracellular pH is crucial to the control of many cellular processes such as glycolysis, protein synthesis, and cell division. To study the relation between intracellular pH and mitotic activity in actively dividing Con A- or LPS-stimulated splenic lymphocytes, a method was developed to determine intracellular pH using a fluorescence-activated cell sorter. The new method uses the pH-sensitive fluorochrome, 4-methylumbelliferone. Results obtained with it not only correspond qualitatively with the results obtained using 14C-dimethyloxazolidinedione (DMO) but also clearly show the active and inactive subpopulations. The intracellular pH of mitogen-stimulated murine lymphocytes increases from pH 7.15 to pH 7.45 when the population has greatest mitotic activity. The intracellular pH of three virus-transformed lymphocyte cell lines is higher by approximately 0.5 pH units when the cells are in exponential growth compared to stationary phase.

Membrane potential of Plasmodium-infected erythrocytes

The membrane potential (Em) of normal and Plasmodium chabaudi-infected rat erythrocytes was determined from the transmembrane distributions of the lipophilic anion, thiocyanate (SCN), and cation, triphenylmethylphosphonium (TPMP). The SCN- and TPMP-measured Em of normal erythrocytes are -6.5 +/- 3 mV and -10 +/- 4 mV, respectively. The TPMP-measured Em of infected cells depended on parasite developmental stage; "late" stages (schizonts and gametocytes) were characterized by a Em = -35 mV "early stages (ring and copurifying noninfected) by a low Em (-16 mV). The SCN-determined Em of infected cells was -7 mV regardless of parasite stage. Studies with different metabolic inhibitors including antimycin A, a proton ionophore (carbonylcyanide m-chlorophenylhydrazone [CCCP] ), and a H+ -ATPase inhibitor (N,N'-dicyclohexylcarbodiimide, [DCCD] ) indicate that SCN monitors the Em across the erythrocyte membrane of infected and normal cells whereas TPMP accumulation reflects the Em across the plasma membranes of both erythrocyte and parasite. These inhibitor studies also implicated proton fluxes in Em-generation of parasitized cells. Experiments with weak acids and bases to measure intracellular pH further support this proposal. Methylamine distribution and direct pH measurement after saponin lysis of erythrocyte membranes demonstrated an acidic pH for the erythrocyte matrix of infected cells. The transmembrane distributions of weak acids (acetate and 5,5-dimethyloxazolidine-2,4-dione) indicated a DCCD-sensitive alkaline compartment. The combined results suggest that the intraerythrocyte parasite Em and delta pH are in part the consequence of an electrogenic proton pump localized to the parasite plasma membrane.

Intracellular pH of mitogen-stimulated lymphocytes

Mitogenic stimulation of mouse lymphocytes results in two sequential intracellular alkalinizations. The first shift of intracellular pH from 7.18 to 7.35 coincides with early biochemical events following mitogenic stimulation. The second alkalinization begins 12 hours after stimulation and rises in parallel with the rate of thymidine incorporation. The results suggest that intracellular alkalinization following stimulation may play a key role in the enhancement of cellular activation and mitogenesis.

Calcium binding to plasma membranes from normal and SV40 transformed hamster lymphocytes

The calcium binding properties of isolated plasma membranes from normal and SV40 transformed hamster lymphocytes were compared over the Ca2+ concentration range of 10(-5)M to 5 x 10(-3)M and at physiological ionic strength. At all Ca2+ concentrations, normal membranes bound more Ca2+ than tumor membranes; at blood Ca2+ levels (1-2 mM) plasma membranes of normal cells bind twice as much as membranes from tumor cells. Normal plasma membranes demonstrated positive cooperative Ca2+ binding whereas tumor membranes displayed non-interacting Ca2+ binding sites. Ca2+ binding to both membranes was insensitive to Mg2+ (0.1 to 2.5 mM). A pH shift from 7 to 6 resulted in a 70% decrease of normal membrane-bound Ca2+ compared to a 40% decrease observed with tumor membranes. Extracellular surface Ca2+ binding to intact cells was also studied after a 72-hour equilibration of cells with 45 Ca2+ and with ethyleneglycol-bis-(beta-amino-ethyl ether) N,N'-tetraacetate chelation as marker for surface Ca2+. Tumor cell surface Ca2+ binding was only 10% of that observed with quiescent lymphocytes. Normal lymphocytes stimulated to divide with phytohemagglutinin also showed a decreased level of surface Ca2+ (50%). However, plasma membranes isolated from non-dividing and phytohemagglutinin-stimulated lymphocytes exhibited equivalent Ca2+ binding.