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R D Prusch

Publications and source records attributed to R D Prusch.

17 recordsLinked to original sources
PubMed1993

A possible signal-coupling role for cyclic AMP during endocytosis in Amoeba proteus.

Cytoplasmic levels of cAMP in Amoeba proteus were measured utilizing radioimmunoassays under control conditions and when stimulated by inducers of either pinocytosis or phagocytosis. In control cells, cytoplasmic cAMP levels were approximately 0.39 pM/mg cells. When exposed to either chemotactic peptide or mannose which stimulate phagocytosis in the amoeba, there is a rapid doubling of the cAMP level within 45 sec of stimulation which then returns to the control level within 3-5 min. Theophylline prolongs the elevation of cytoplasmic cAMP in stimulated cells and is also capable of eliciting food vacuole formation in the amoeba. In addition isoproterenol also causes food vacuole formation in the amoeba as well as a large and prolonged increase in cytoplasmic cAMP levels. Inducers of pinocytosis (BSA and Na Cl) also elicit changes in cytoplasmic cAMP in the amoeba, but the response appears to differ from that elicited by inducers of phagocytosis in that the peak cAMP levels are broader and biphasic. It is concluded that cAMP plays a signal-coupling role during the early phases of both forms of endocytosis in Amoeba proteus.

Amoeba↗
PubMed1989

Prostaglandins may play a signal-coupling role during phagocytosis in Amoeba proteus.

Phagocytosis in Amoeba proteus can be induced with prostaglandins (PG). In addition, arachidonic acid (the fatty acid precursor to the PG-2 series) also induces phagocytosis. The induction of phagocytosis with arachidonic acid can be partially inhibited by the cyclooxygenase inhibitor indomethacin. Phagocytosis in the amoeba can also be induced with the chemotactic peptide N-formylmethionyl-leucylphenylalanine (NFMLP). The peptide presumably induces phagocytosis by interacting with receptors on the amoeba surface, which may initiate the release of arachidonic acid from membrane lipids. NFMLP-induced phagocytosis can also be partially inhibited by indomethacin. It is suggested that PG's or biochemically related substances may play a signal-coupling role during phagocytosis in the amoeba.

Amoeba↗
PubMed1986

Calcium and initial surface binding phase of pinocytosis in Amoeba proteus.

The uptake of membrane-bound solute and external medium by bulk-phase pinocytosis in Amoeba proteus is influenced by the level of Ca2+ in the external medium. Increasing external Ca2+ to approximately 10(-4) M increases pinocytotic intensity, while increases in Ca2+ above this level decrease the intensity of pinocytosis. The initial interaction of pinocytotic inducers and Ca2+ at the surface of Amoeba proteus was therefore examined. Alcian blue and Na+, both inducers of pinocytosis, differ in the manner with which they associate with the amoeba surface, suggesting the possibility of different pinocytosis-inducing sites on the amoeba surface. Low levels of external Ca2+ in the range of 3 X 10(-5) to 1.5 X 10(-4) M increase the amount of cationic inducer associated with the cell surface while, at the same time, decreasing anion association with the cell surface. It is suggested that Ca2+ influences ion association with the cell surface by controlling the availability of negative surface sites, which in turn influences pinocytotic intensity.

Alcian Blue↗
PubMed1983

Characterization of a DFP-hydrolyzing enzyme in squid posterior salivary gland by use of Soman, DFP and manganous ion.

1. A phosphorus-fluorine splitting enzyme (DFPase) from squid nerve hydrolyzes DFP 5-10 times faster than it hydrolyzes another P-F compound, Soman, whereas a superficially similar enzyme from rat kidney hydrolyzes Soman 20-40 times faster than it hydrolyzes DFP, all under comparable conditions. 2. The DFPase from rat kidney is stimulated 2- to 3-fold by 4 X 10(-4) M Mn2+, whereas the DFPase from squid nerve is unaffected or slightly inhibited by 4 X 10(-4) M Mn2+. 3. These observations form the basis for distinguishing between a squid type DFPase and a mammalian DFPase, the names not being rigorously indicative of enzyme source or substrate. 4. When these criteria are applied to a P-F splitting enzyme found in squid saliva, the enzyme is identifiable as squid type DFPase. There is a significantly higher level of this enzyme in whole saliva from female squids than in whole saliva from male squids. This squid type DFPase is different from the proteinous toxin also found in squid saliva.

Animals↗
PubMed1981

Bulk solute extrusion as a mechanism conferring solute uptake specificity by pinocytosis in Amoeba proteus.

A variety of positively charged solutes induce pinocytosis in Amoeba proteus, ranging from metabolically useful material to solutes that may prove harmful, such as Alcian blue. Alcian blue is taken up by pinocytosis and then a fraction of the accumulated dye is expelled in bulk form through "extrusion channels." This response is not elicited by other solutes taken up by pinocytosis in the amoeba, implying that if any selectivity is associated with this process, it is by specific solute extrusion mechanisms in the cytoplasm.

Alcian Blue↗
PubMed1980

Endocytotic sucrose uptake in Amoeba proteus induced with the calcium ionophore A23187.

The calcium ionophore A23187 brings about an influx of calcium and uptake of sucrose by endocytosis in Amoeba proteus. The amount of endocytotic sucrose uptake elicited by the ionophore depends upon the external calcium ion concentration. Calcium ion movements may serve to couple the surface phase of endocytosis with cytoplasmic uptake of the endocytotic inducer.

Amoeba↗
PubMed1979

Calcium distribution in Amoeba proteus.

A preliminary investigation of the distribution of cellular calcium in Amoeba proteus was undertaken. Total cellular calcium under control conditions was found to be 4.59 mmol/kg of cells. When the external Ca++ concentration is increased from the control level of 0.03 to 20 mM, a net Ca++ influx results with a new steady-state cellular calcium level being achieved in integral of 3 h. At steady state the amount of calcium per unit weight of cells is higher than the amount of calcium per unit weight of external solution when the external concentration of Ca++ is below 10 mM. At external Ca++ concentrations above this level, total cellular calcium approaches the medium level of Ca++. Steady-state calcium exchange in Amoeba proteus was determined with 45Ca. There is an immediate and rapid exchange of integral of 0.84 mmol/kg of cells or 18% of the total cellular calcium with the labelled Ca++. Following this initial exchange, there was very little if any further exchange observed. Most of this exchanged calcium could be eliminated from the cell with 1 mM La+++, suggesting that the exchanged calcium is associated with the surface of the cell. Increase in either the external Ca++ concentration of pH raise the amount of exchangeable calcium associated with the cell. Calcium may be associated with the cell surface as a co-ion in the diffuse double layer or bound to fixed negative sites on the surface of the cell. If Ca++-binding sites do exist on the cell surface, there may be more than one type and they may have different dissociation constants. The cytoplasmic Ca++ ion activity is probably maintained at very low levels.

Amoeba↗
PubMed1979

Sucrose uptake by pinocytosis in Amoeba proteus and the influence of external calcium.

The relationship between Ca++ and pinocytosis was investigated in Amoeba proteus. Pinocytosis was induced with 0.01% alcian blue, a large molecular weight dye which binds irreversibly to the cell surface. The time-course and intensity of pinocytosis was monitored by following the uptake of [3H]SUCROSE. When the cells are exposed to 0.01% alcian blue, there is an immediate uptake of sucrose. The cells take up integral of 10% of their initial volume during the time-course of pinocytosis. The duration of pinocytosis in the amoeba is integral of 50 min, with maximum sucrose uptake occurring 15 min after the induction of pinocytosis. The pinocytotic uptake of sucrose is reversibly blocked at 3 degrees C and a decrease in pH increases the uptake of sucrose by pinocytosis. The process of pinocytosis is also dependent upon the concentration of the inducer in the external medium. The association between Ca++ and pinocytosis in A. proteus was investigated initially by determining the effect of the external Ca++ concentration on sucrose uptake induced by alcian blue. In Ca++-free medium, no sucrose uptake is observed in the presence of 0.01% alcian blue. As the Ca++ concentration is increased, up to a maximum of 0.1 mM, pinocytotic sucrose uptake is also increased. Increases in the external Ca++ concentration above 0.1 mM brings about a decrease in sucrose uptake. Further investigations into the association between Ca++ and pinocytosis demonstrated that the inducer of pinocytosis displaces surface calcium in the amoeba. It is suggested that Ca++ is involved in two separate stages in the process of pinocytosis; an initial displacement of surface calcium by the inducer which may increase the permeability of the membrane to solutes and a subsequent Ca++ influx bringing about localized increases in cytoplasmic Ca++ ion activity.

Amoeba↗
PubMed1976

Unidirectional ion movements in the hindgut of larval Sarcophaga bullata (Diptera: Sarcophagidae).

1. Unidirectional Na+, K+, and Cl- fluxes were measured across the isolated hindgut of larval Sarcophaga bullata. 2. Both K+ and Cl- are actively secreted into the hindgut lumen, whereas Na+ is distributed passively. 3. The movements of K+ and Cl- are not entirely independent of each other, and the movement of one ion influences the flux of the co-ion. 4. The NH4+ ion is secreted into the hindgut by a mechanism separate from K+ secretion.

Ammonia↗