scholarly journals Na+/Pi co-transport alters rapidly cytoskeletal protein polymerization dynamics in opossum kidney cells

1996 ◽  
Vol 315 (1) ◽  
pp. 241-247 ◽  
Author(s):  
Evangelia A. PAPAKONSTANTI ◽  
Dimitrios S. EMMANOUEL ◽  
Achille GRAVANIS ◽  
Christos STOURNARAS
Keyword(s):  
Immunoblot Analysis ◽  
Kidney Cells ◽  
Opossum Kidney ◽  
Protein Polymerization ◽  
Phosphonoformic Acid ◽  
Opossum Kidney Cells ◽  
Proximal Tubular ◽  
Microtubule Stabilizer ◽  
Dynamic Equilibria ◽  
Contrast Measurement

We studied with biochemical and immunofluorescent techniques the interactions between the actin microfilament and tubulin microtubule cytoskeleton and Na+/Pi co-transport in opossum kidney cells, a line with proximal tubular characteristics. On brief (5 min) incubation of the cells with a low (0.1 mM) concentration of Pi, a rapid F-actin depolymerization takes place, which fails to occur in cells incubated under similar conditions with 1 mM Pi. The disassembly of actin microfilaments could be quantitatively expressed as a 33% increase in the ratio of monomeric G-actin to polymerized F-actin (G/F-actin ratio from 0.80±0.03 to 1.06±0.06, n = 28, P < 0.01), owing to a significant decrease in the latter. Under these conditions microfilaments were also markedly destabilized, as shown by their diminished resistance to graded cytochalasin B concentrations. In addition, incubation of opossum kidney cells with low Pi concentrations (0.1 mM) resulted within 5 min in a substantial depolymerization of microtubules, shown by immunofluorescence microscopy and measured as a 70.9±6.9% (n = 11, P < 0.01) decrement by immunoblot analysis. These changes, which occur only when extracellular Pi concentrations are kept low, seem to be related to a significant increase within 5 min in the rate of cellular Pi uptake by 25.5% under these conditions. The shifts in the dynamic equilibria between monomeric and polymerized actin and tubulin in response to cellular Pi uptake were transient, being fully reversible within 30 min. Moreover, the effect of Pi seemed to be specific because inhibition of its uptake by phosphonoformic acid blunted microtubular disassembly markedly. In contrast, measurement of Pi uptake in the presence of agents known to stabilize cytoskeletal structures showed a substantial decrease with phallacidin, which stabilizes microfilaments, whereas the microtubule stabilizer taxol had no apparent effect. These results indicate that acute alterations in the polymerization dynamics and stability of both microfilaments and microtubules are involved in the modulation of Na+/Pi co-transport and suggest important cytoskeletal participation in proximal tubular transport functions.

scholarly journals Long-term protein exposure reduces albumin binding and uptake in proximal tubule-derived opossum kidney cells.

1998 ◽  
Vol 9 (6) ◽  
pp. 960-968 ◽  
Author(s):  
M Gekle ◽  
S Mildenberger ◽  
R Freudinger ◽  
S Silbernagl
Keyword(s):  
Amino Acids ◽  
Proximal Tubule ◽  
Uptake Rate ◽  
Kidney Cells ◽  
Proximal Tubular Cells ◽  
Opossum Kidney ◽  
Tubular Cells ◽  
Opossum Kidney Cells ◽  
Proximal Tubular ◽  
Protein Reabsorption

To avoid renal loss of large amounts of proteins, filtered proteins are reabsorbed by endocytosis along the proximal tubule. However, although protein reabsorption is a task of proximal tubular cells, it is also a threat because it may cause cell injury. This study determines whether exposure to bovine serum albumin (BSA) leads to regulatory changes in endocytosis of FITC-BSA in proximal tubule-derived opossum kidney cells. Preincubation with BSA led to a decrease of FITC-BSA endocytosis with an IC50 value of 0.58 g/L. Specific binding of FITC-BSA to the apical membrane was also reduced (IC50 = 0.69 g/L). Kinetic analyses revealed that maximal uptake rate and maximal binding capacity were decreased with no change in affinity. Similar effects were observed after preincubation with equimolar amounts of other proteins (lactalbumin, transferrin, and conalbumin), but not after preincubation with dextran. The effect of preincubation with BSA could be mimicked by preincubation with some amino acids. Preincubation with L-Ala, L-Gln, or NH4Cl, but not with L-Leu, L-Glu, or L-Asp, reduced FITC-BSA endocytosis and binding. Preincubation with BSA, but not with dextran, reduced protein degradation and increased ammonia production, vesicular pH, as well as the rate of lactate dehydrogenase release. Apical fluid-phase endocytosis and apical uptake of neutral amino acids were not reduced. It is concluded that proximal tubular cells reduce the uptake rate for proteins, but not for other substrates, in response to increased protein load. This reduction is achieved by reducing the number of apical binding sites, partially in response to increased ammoniagenesis with deranged vesicular pH and enzyme activities. Thus, increased protein filtration could result in reduced protein reabsorption, thereby enhancing proteinuria.

scholarly journals Adaptation of Opossum Kidney Cells to Luminal Phosphate: Effects of Phosphonoformic Acid and Kinase Inhibitors

2016 ◽  
Vol 41 (3) ◽  
pp. 298-310 ◽  
Author(s):  
Linto Thomas ◽  
Carsten A. Wagner ◽  
Jürg Biber ◽  
Nati Hernando
Keyword(s):  
Kinase Inhibitors ◽  
Kidney Cells ◽  
Opossum Kidney ◽  
Phosphonoformic Acid ◽  
Opossum Kidney Cells

Calcitriol stimulates Na(+)-Pi cotransport in a subclone of opossum kidney cells (OK-7A) by a genomic mechanism

1993 ◽  
Vol 264 (3) ◽  
pp. F404-F410 ◽  
Author(s):  
M. Allon ◽  
M. Parris
Keyword(s):  
Kidney Cells ◽  
Dihydroxyvitamin D3 ◽  
Prolonged Incubation ◽  
Opossum Kidney ◽  
Ok Cells ◽  
Opossum Kidney Cells ◽  
Proximal Tubular ◽  
Renal Proximal Tubular Cells ◽  
Renal Proximal Tubular ◽  
Contrast Ct

Calcitriol (CT) stimulates Na(+)-Pi cotransport in a subclone of opossum kidney cells (OK-7A) by a genomic mechanism. An experimental model of renal proximal tubular cells in which CT affects Na(+)-Pi cotransport would be useful for examining the mechanisms of this effect. This study evaluated the effect of CT on Na(+)-Pi cotransport in opossum kidney (OK) cells. CT had no effect on Na(+)-Pi cotransport in wild-type OK cells and in the OK-B, OK-H, and OK-P subclones. In contrast, CT at physiological concentrations stimulated Na(+)-Pi cotransport in the OK-7A subclone; the effect was dose related with a 52% increase at 10(-11) M CT, as well as a maximal twofold stimulation at 10(-9) M. CT (10(-11) M) increased the maximum uptake for Na(+)-Pi cotransport (Vmax = 3.55 +/- 0.16 vs. 2.51 +/- 0.17 nmol.mg protein-1.5 min-1, P < 0.01), without affecting the apparent Michaelis constant (Km = 30.6 +/- 1.0 vs. 30.8 +/- 0.7 microM). The stimulatory effect on Na(+)-Pi cotransport was specific for CT and did not occur with 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or 1 beta,25-dihydroxyvitamin D3. At 10(-11) M CT, the stimulation of Na(+)-Pi uptake in OK-7A cells was maximal at 3 h; it was completely abolished by preincubation with actinomycin D or cycloheximide. Both calphostin C, an inhibitor of protein kinase C (PKC), or prolonged incubation with phorbol 12-myristate 13-acetate, to downregulate the PKC pathway, partially inhibited the stimulatory effect of CT on Na(+)-Pi cotransport in OK-7A cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for interference of vitamin D with PTH/PTHrP receptor expression in opossum kidney cells

1998 ◽  
Vol 436 (2) ◽  
pp. 289-294 ◽  
Author(s):  
H. Wald ◽  
Michal Dranitzki-Elhalel ◽  
R. Backenroth ◽  
Mordecai M. Popovtzer
Keyword(s):  
Vitamin D ◽  
Receptor Expression ◽  
Kidney Cells ◽  
Opossum Kidney ◽  
Opossum Kidney Cells ◽  
Pthrp Receptor
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