188 research outputs found
Functional asymmetry in phosphate transport and its regulation in opossum kidney cells: parathyroid hormone inhibition.
No full textThe sidedness (apical vs basolateral) of the inhibitory of phosphate (Pi) transport by parathyroid hormone (PTH) was investigated in opossum kidney (OK)-cell monolayers grown on permeant support. PTH was found to regulate the activity of only the apical Na Pi cotransporter, having no effect on the basolateral transport systems. Transport inhibition was approximately 100-fold more sensitive to apical PTH application (Kd: 5 x 10(-12) M) than to basolateral application (Kd: 5 x 10(-10) M). The time-course of the inhibitory response was identical from the two cell surfaces, with half-maximum inhibition occurring at about 20 min and almost full inhibition by 90 min. Experiments on diffusion and degradation demonstrated that the difference in Kd at the two cell surfaces was not due to differential metabolism or diffusion. Tests of cooperativity between the apical and basolateral regulatory events at intermediate concentrations suggested that the presence of PTH on one side of the monolayer reduced the scope of response from the other side. At maximum doses of PTH (10(-7)-10(-8) M) the transport inhibition from either side was equal and not additive. We conclude that in OK-cell monolayers grown on permeant support only apical Na/Pi co-transport is sensitive to PTH inhibition and that PTH receptor properties may be different on the apical and basolateral surfaces
Functional asymmetry of phosphate transport and its regulation in opossum kidney cells: phosphate transport.
No full textThe polarized distribution of phosphate (Pi) transport systems in a continuous renal cell line derived from opossum kidney (OK) was measured in monolayers grown on permeant filter support. When cultured on collagen-coated nitrocellulose filters, OK cells formed tight, functionally polarized monolayers. Three Pi transport systems were identified in these monolayers: one apical sodium (Na)-dependent system and two systems on the basolateral surface, one Na-dependent and one Na-independent. The apical system was high-affinity (Km = 0.4 mM Pi), low-capacity (Jmax = 1100 pmol Pi/mg protein per minute) with a Na:Pi stoichiometry greater than 1 (n = 3) and a high interaction coefficient (KNa = 105 mM Na). On the basolateral surface the Na-independent system comprised about 30% of the total Pi transport at this surface. Both basolateral systems were of low affinity (Km: Na-independent, 2.6 mM; Na-dependent, 5.2 mM) and high capacity (Jmax: Na-independent, 2100; Na-dependent, 2400 pmol/mg protein per minute). The basolateral Na-dependent system had a Nai stoichiometry of 1 and a relatively low interaction coefficient (KNa = 25 mM Na). Only the basolateral Na-independent system was inhibitable by 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS). These results are compatible with a net vectorial transcellular transport of Pi from the apical through the basolateral cell surfaces. The presence of a basolateral Na-dependent system may reflect additional metabolic requirements that cannot be met only by apical influx. Taken together, these results demonstrate the ability to grow cell monolayers successfully, displaying polarized transport activities similar to in situ
Role of pHi, and proton transporters in oncogene-driven neoplastic transformation
No full textThe change of a normal, healthy cell to a transformed cell is the first step in the evolutionary arc of a cancer. While the role of oncogenes in this 'passage' is well known, the role of ion transporters in this critical step is less known and is fundamental to our understanding the early physiological processes of carcinogenesis. Cancer cells and tissues have an aberrant regulation of hydrogen ion dynamics leading to a reversal of the normal tissue intracellular to extracellular pH gradient (ΔpHi to ΔpHe). When this perturbation in pH dynamics occurs during carcinogenesis is less clear. Very early studies using the introduction of different oncogene proteins into cells observed a concordance between neoplastic transformation and a cytoplasmic alkalinization occurring concomitantly with a shift towards glycolysis in the presence of oxygen, i.e. 'Warburg metabolism'. These processes may instigate a vicious cycle that drives later progression towards fully developed cancer where the reversed pH gradient becomes ever more pronounced. This review presents our understanding of the role of pH and the NHE1 in driving transformation, in determining the first appearance of the cancer 'hallmark' characteristics and how the use of pharmacological approaches targeting pH/NHE1 may open up new avenues for efficient treatments even during the first steps of cancer development
Intestinal glycyl-L-phenylalanine and L-phenylalanine transport in a euryhaline teleost
No full textThe transport mechanisms for the dipeptide glycyl-L-phenylalanine (Gly-Phe) and L-phenylalanine (Phe) were characterized in fish intestinal brush-border membrane vesicles (BBMV). Gly-Phe was rapidly hydrolyzed only intravesicularly with almost total hydrolysis occurring even at 10 s. Dipeptide uptake was not stimulated by an inward gradient of Na, K, or H. Phe uptake was stimulated by an inward gradient of either Na or K but displayed an overshoot phenomenon only in the presence of an Na gradient. Kinetic analysis of the effect of substrate concentration on transport rate revealed that transport of both Gly-Phe and Phe occurred by a saturable process conforming to Michaelis-Menten kinetics. The K(m) for Gly-Phe was 9.8 ± 3.5 mM, whereas that for Phe in the presence of Na or K, respectively, was 0.74 ± 0.13 and 1.1 ± 0.37 mM. Maximum uptake for Gly-Phe and for Phe in the presence of Na and K was 5.1, 0.9, and 0.4 nmol·mg and protein-1·5 s-1, respectively. Gly-Phe and Phe transport displayed different patterns of inhibition by dipeptides and amino acids. These results suggest that Gly-Phe and Phe are transported via different mechanisms, with Gly-Phe being hydrolyzed during a carrier-mediated, cation-independent process and Phe being transferred via a Na+ cotransport process similar to that described in mammals. During conditions of high luminal dipeptide concentrations, the Gly-Phe pathway may make a significant contribution to total Phe uptake
The role of disturbed pH dynamics and the Na+/H+ exchanger in metastasis
No full textRecent research has highlighted the fundamental role of the tumour's extracellular metabolic microenvironment in malignant invasion. This microenvironment is acidified primarily by the tumour-cell Na+/H+ exchanger NHE1 and the H+/lactate cotransporter, which are activated in cancer cells. NHE1 also regulates formation of invadopodia - cell structures that mediate tumour cell migration and invasion. How do these alterations of the metabolic microenvironment and cell invasiveness contribute to tumour formation and progression
Intestinal glucose transport and salinity adaptation in a euryhaline teleost
No full textGlucose transport by upper and lower intestinal brush-border membrane vesicles of the African tilapia (Oreochromis mossambicus) was characterized in fish acclimated to either freshwater or full-strength seawater. D-[3H]-glucose uptake by vesicles was stimulated by a transmembrane Na gradient, was electrogenic, and was enhanced by counter-transport of either D-glucose or D-galactose. Glucose transport was greater in the upper intestine than in the lower intestine and in seawater animals rather than in fish acclimated to freshwater. Glucose influx (10-s uptake) involved both saturable and nonsaturable transport components. Seawater adaptation increased apparent glucose influx K(t), J(max), apparent diffusional permeability (P), and the apparent Na affinity of the cotransport system in both intestinal segments, but the stoichiometry of Na-glucose transfer (1:1) was unaffected by differential saline conditions or gut region. It is suggested that increased sugar transport in seawater animals is due to the combination of enhanced Na-binding properties and an increase in number of transfer rate of the transport proteins. Freshwater animals compensate for reduced Na affinity of the coupled process by markedly increasing the protein affinity for glucose
Differential responsiveness of proliferation and cytokeratin release to stripped serum and oestrogen in the human breast cancer cell line, MCF-7.
No full textIn vitro research into hormone sensitivity and the relation to proliferation of cytokeratin release from cancer cells is scarce. Therefore, we examined the stimulation of proliferation and the release of cytokeratins in a breast cancer cell culture model. Cell growth was stimulated by 17 beta-oestradiol (10(-11) M), stripped serum (10%) and by the two together. Cytokeratin release was stimulated only by stripped serum, oestradiol having no effect. After long incubation periods (> 12 h), cytokeratin release also commenced in the control and oestradiol treatments. Release rate versus time analysis suggested that there are two different release processes. Cytokeratin release was first stimulated at a stripped serum concentration approximately 100 times lower than that which initiated proliferation. Pharmacological alteration of proliferation with cordyceptin resulted in growth changes without alterations in cytokeratin release. We conclude that cytokeratin release in these cells is unrelated to proliferation, independent of oestrogen action and probably in some way related to growth factor receptor function
Brush-border inositol transport by intestines of carnivorous and herbivorous teleosts
No full textTransport characteristics of myoinositol by isolated brush-border membrane vesicles of two fish, the herbivorous tilapia (Oreochromis mossambicus) and the carnivorous eel (Anguilla anguilla), were measured. [3H]myoinositol uptake by vesicles of both fish was stimulated by a transmembrane Na gradient, was electrogenic, and was inhibited by phloridzin. Kinetic analysis of myoinositol influx disclosed species differences (tilapia, K = 0.15 mM, J(max) = 0.2 nmol·mg protein-1·min-1; eel, K = 2.6 mM, J(max) = 0.8 nmol·mg protein-1·min-1). D-Glucose inhibition of myoinositol influx was shown to be noncompetitive. Additional inhibition studies with a range of sugars demonstrated that aldohexoses in the C-1 chair conformation were preferred substrates. Myoinositol had no effect on D-glucose transport. Preloading vesicles with myoinositol transstimulated [3H]myoinositol uptake, while the use of internal D-glucose was without effect. These results suggest that the intestinal brush border may have a pathway for myoinositol transport entirely separate from that for D-glucose but inhibited by D-glucose via binding to a regulator site on the myoinositol transporter. Markedly dissimilar influx kinetic constants suggest possible differences in myoinositol needs by carnivorous and herbivorous fish
- …
