An NMR study of cellular phosphates and membrane transport in renal proximal tubules

1995 ◽  
Vol 268 (3) ◽  
pp. F375-F384 ◽  
Author(s):  
M. C. Chobanian ◽  
M. E. Anderson ◽  
P. C. Brazy
Keyword(s):  
Membrane Potential ◽  
Membrane Transport ◽  
Basolateral Membrane ◽  
Barium Chloride ◽  
Partial Replacement ◽  
Transport Mechanisms ◽  
Extracellular Medium ◽  
Protein Inhibition ◽  
Nmr Study ◽  
Perifusion System

Technical limitations in the measurement of cellular phosphates have hindered studies of interrelationships between cellular Pi, its transport, and its metabolism in renal proximal tubule (PT) cells. We have developed a noninvasive 31P-nuclear magnetic resonance (NMR) probe-perifusion system to measure cellular Pi and have utilized this system to investigate relationships in canine PT cells between the membrane transport and the cellular content of Pi. With 1.2 mM Pi in the extracellular medium, the cellular Pi content of PT averaged 4.94 +/- 0.55 nmol/mg protein. Inhibition of Pi uptake by removal of extracellular Pi rapidly decreased all cellular phosphate compounds to values that were between 55 and 85% of control. Partial replacement of extracellular Pi (0.4 mM) increased cellular phosphates up to 84-100% of control values. Inhibition of Na(+)-K(+)-adenosinetriphosphatase uptake by the addition of ouabain failed to change either cellular Pi or organic phosphates. Reducing the basolateral membrane potential with the addition of barium chloride increased cellular Pi content by nearly 30%. Maximal contents of cellular Pi and ATP were achieved at 0.4 mM Pi in the presence of an inwardly directed Na+ gradient and at 0.8 mM Pi in its absence. These data indicate that cellular Pi content in canine PT is regulated by Na(+)-dependent and -independent transport mechanisms and by the membrane potential across the basolateral membrane. Lastly, cellular ATP content was found to be directly proportional to the cellular Pi content over a physiological range.

Carrier-mediated transport of tetraethylammonium across rabbit renal basolateral membrane

1989 ◽  
Vol 257 (2) ◽  
pp. F243-F251 ◽  
Author(s):  
C. Montrose-Rafizadeh ◽  
F. Mingard ◽  
H. Murer ◽  
F. Roch-Ramel
Keyword(s):  
Membrane Potential ◽  
Exchange Reaction ◽  
Brush Border ◽  
Renal Cortex ◽  
Basolateral Membrane ◽  
Organic Cations ◽  
Transport Mechanisms ◽  
Carrier Mediated Transport ◽  
S Uptake ◽  
Similar Affinity

Mechanisms of tetraethylammonium (TEA) transport were investigated in basolateral membrane (BLM) vesicles from rabbit renal cortex. Preloading vesicles with 10 mM TEA or 1 mM mepiperphenidol stimulated the 15-s uptake of [14C]-TEA compared with control vesicles (258 and 200%, respectively) and produced an overshoot of the equilibrium value (3 and 1.6 times, respectively). In the presence of a K+ gradient, net TEA uptake was also increased (and showed an overshoot of 2-fold) when the membrane potential of vesicles was made interior negative by adding valinomycin. Both TEA-TEA exchange and the voltage-driven net TEA transport were cis-inhibited by other organic cations, and a similar affinity order was found for both transport mechanisms (quinine greater than amiloride greater than morphine greater than mepiperphenidol greater than choline = N1-methylnicotinamide). This data suggests that the same transport protein might be responsible for both phenomena. Other experiments determined that the BLM vesicles had no TEA-H+ exchange, and that contamination of the vesicle population by brush-border membranes was negligible in terms of their contribution to TEA transport. These results demonstrate the presence of an exchange reaction for TEA in the rabbit renal BLM and thus imply carrier-mediated transport of TEA by these membranes.

The involvement of selected membrane transport mechanisms in the cellular uptake of 177Lu-labeled bombesin, somatostatin and gastrin analogues

2015 ◽  
Vol 42 (1) ◽  
pp. 1-7 ◽  
Author(s):  
M. Volková ◽  
J. Mandíková ◽  
A. Lázníčková ◽  
M. Lázníček ◽  
P. Bárta ◽  
...  
Keyword(s):  
Membrane Transport ◽  
Cellular Uptake ◽  
Transport Mechanisms

scholarly journals Integration of computational modeling with membrane transport studies reveals new insights into amino acid exchange transport mechanisms

2015 ◽  
Vol 29 (6) ◽  
pp. 2583-2594 ◽  
Author(s):  
Kate L. Widdows ◽  
Nuttanont Panitchob ◽  
Ian P. Crocker ◽  
Colin P. Please ◽  
Mark A. Hanson ◽  
...  
Keyword(s):  
Amino Acid ◽  
Computational Modeling ◽  
Membrane Transport ◽  
Transport Mechanisms ◽  
Amino Acid Exchange ◽  
Transport Studies ◽  
Acid Exchange

Inhibition of P-glycoprotein-mediated transport by a hydrophobic contaminant in commercial gluconate salts

1999 ◽  
Vol 276 (6) ◽  
pp. C1439-C1442 ◽  
Author(s):  
Carlos G. Vanoye ◽  
Guillermo A. Altenberg ◽  
Luis Reuss
Keyword(s):  
Membrane Transport ◽  
Ringer Solution ◽  
Chloroform Extract ◽  
Rhodamine 123 ◽  
Transport Mechanisms ◽  
Sodium Gluconate ◽  
Chloroform Extraction ◽  
P Glycoprotein ◽  
Dependent Transport

The substitution of gluconate for Cl− is commonly used to characterize Cl− transport or Cl−-dependent transport mechanisms. We evaluated the effects of substituting gluconate for Cl− on the transport of the P-glycoprotein substrate rhodamine 123 (R123). The replacement of Ringer solution containing Cl−(Cl−-Ringer) with gluconate-Ringer inhibited R123 efflux, whereas the replacement of Cl− by other anions (sulfate or cyclamate) had no effect. The inhibition of R123 efflux by gluconate-Ringer was absent after chloroform extraction of the sodium gluconate salt. The readdition of the sodium gluconate-chloroform extract to the extracted gluconate-Ringer or to cyclamate-Ringer inhibited R123 efflux, whereas its addition to Cl−-Ringer had no effect. These observations indicate that the inhibition of P-glycoprotein-mediated R123 transport by gluconate is due to one or more chloroform-soluble contaminants and that the inhibition is absent in the presence of Cl−. The results are consistent with the fact that P-glycoprotein substrates are hydrophobic. Care should be taken when replacing ions to evaluate membrane transport mechanisms because highly pure commercial preparations may still contain potent contaminants that affect transport.

Inhibition of Na+/H+exchange stimulates CCK secretion in STC-1 cells

1998 ◽  
Vol 275 (4) ◽  
pp. G689-G695
Author(s):  
Veronica Prpic ◽  
J. Gregory Fitz ◽  
Yu Wang ◽  
John R. Raymond ◽  
Maria N. Garnovskaya ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Cell Metabolism ◽  
Hormone Secretion ◽  
Membrane Depolarization ◽  
Ph Sensitive ◽  
Extracellular Medium ◽  
Voltage Dependent ◽  
Effects Of Ph ◽  
Intracellular Ca ◽  
Cck Release

It has been demonstrated that K+ channel regulation of membrane potential is critical for control of CCK secretion. Because certain K+ channels are pH sensitive, it was postulated that pH affects K+channel activity in the CCK-secreting cell line STC-1 and may participate in regulating CCK secretion. The present study examines the role of electroneutral Na+/H+exchange on extracellular acidification and hormone secretion. Treatment of STC-1 cells with the amiloride analog ethylisopropyl amiloride (EIPA) to inhibit Na+/H+exchange inhibited Na+-dependent H+ efflux and increased basal CCK secretion. Substituting choline for NaCl in the extracellular medium elevated basal intracellular Ca2+concentration and stimulated CCK release. Stimulatory effects on hormone secretion were blocked by the L-type Ca2+ channel blocker diltiazem, indicating that secretion was dependent on the influx of extracellular Ca2+. To determine whether the effects of EIPA and Na+ depletion were due to membrane depolarization, we tested graded KCl concentrations. The ability of EIPA to increase CCK secretion was inhibited by depolarization induced by 10–50 mM KCl in the bath. Maneuvers to lower intracellular pH (pHi), including reducing extracellular pH (pHo) to 7.0 or treatment with sodium butyrate, significantly increased CCK secretion. To examine whether pH directly affects membrane K+ permeability, we measured outward currents carried by K+, using whole cell patch techniques. K+ current was significantly inhibited by lowering pHo to 7.0. These effects appear to be mediated through changes in pHi, because intracellular dialysis with acidic solutions nearly eliminated current activity. These results suggest that Na+/H+exchange and membrane potential may be functionally linked, where inhibition of Na+/H+exchange lowers pHi and depolarizes the membrane, perhaps through inhibition of pH-sensitive K+ channels. In turn, K+ channel closure and membrane depolarization open voltage-dependent Ca2+ channels, leading to an increase in cytosolic Ca2+ and CCK release. The effects of pHi on K+ channels may serve as a potent stimulus for hormone secretion, linking cell metabolism and secretory functions.

Succinate alters respiration, membrane potential, and intracellular K+ in proximal tubule

1988 ◽  
Vol 255 (6) ◽  
pp. F1170-F1177 ◽  
Author(s):  
S. R. Gullans ◽  
B. C. Kone ◽  
M. J. Avison ◽  
G. Giebisch
Keyword(s):  
Membrane Potential ◽  
Atpase Activity ◽  
Ion Transport ◽  
Proximal Tubule ◽  
Basolateral Membrane ◽  
Coupling Efficiency ◽  
Atp Synthesis ◽  
Dependent Manner ◽  
Kinetic Evaluation ◽  
Apparent Increase

Succinate, a dicarboxylic acid, is an intermediate in the Krebs cycle that is transported and metabolized by the renal proximal tubule. It is also known to increase proximal tubule transport of phosphate and glucose but not fluid by unknown mechanisms. In the present study, succinate increased proximal tubule respiration in a dose-dependent manner, and a kinetic evaluation indicated that two separate processes were activated. A lower-affinity (Km = 0.9 mM), higher-capacity stimulation (Vmax increase of 49%) was attributed to a decrease in the mitochondrial coupling efficiency. A higher-affinity process (Km = 0.012 mM) was related to an apparent increase in ATP synthesis. The apparent increase in ATP synthesis was not associated with a change in Na+-K+-ATPase activity, however, but rather indicated a 49% increase in ion transport-independent ATP utilization. Basolateral membrane potential hyperpolarized by -7 mV in the presence of succinate, and this was related to an increase in the K+ transference number. Finally, 1 and 5 mM succinate promoted a net cellular uptake of K+, leading to an 11% increase in intracellular K+, which was not the result of an increase in Na+-K+-ATPase activity. Thus the cellular entry and metabolism of succinate promotes multiple changes in ion transport without altering Na+-K+-ATPase activity.

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