Correspondence to: Albrecht Schwab, Physiologisches Institut, Röntgenring 9, D-97070 Würzburg, Germany. Fax:49 931 312741 E-mail:albrecht.schwab{at}mail.uni-wuerzburg.de.
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cell migration is crucial for processes such as immune defense, wound healing, or the formation of tumor metastases. Typically, migrating cells are polarized within the plane of movement with lamellipodium and cell body representing the front and rear of the cell, respectively. Here, we address the question of whether this polarization also extends to the distribution of ion transporters such as Na+/H+ exchanger (NHE) and anion exchanger in the plasma membrane of migrating cells. Both transporters are required for locomotion of renal epithelial (Madin-Darby canine kidney, MDCK-F) cells and human melanoma cells since their blockade reduces the rate of migration in a dose-dependent manner. Inhibition of migration of MDCK-F cells by NHE blockers is accompanied by a decrease of pHi. However, when cells are acidified with weak organic acids, migration of MDCK-F cells is normal despite an even more pronounced decrease of pHi. Under these conditions, NHE activity is increased so that cells are swelling due to the accumulation of organic anions and Na+. When exclusively applied to the lamellipodium, blockers of NHE or anion exchange inhibit migration of MDCK-F cells as effectively as when applied to the entire cell surface. When they are directed to the cell body, migration is not affected. These data are confirmed immunocytochemically in that the anion exchanger AE2 is concentrated at the front of MDCK-F cells. Our findings show that NHE and anion exchanger are distributed in a polarized way in migrating cells. They are consistent with important contributions of both transporters to protrusion of the lamellipodium via solute uptake and consequent volume increase at the front of migrating cells.
Key Words: migration, Na+/H+ exchanger, Cl-/HCO3- exchanger, cell volume, pH
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cell migration plays a central role for such diverse physiological and pathophysiological processes as embryogenesis, wound healing, immune defense, and tumor metastases. A typical feature of migrating cells is their polarization within the plane of movement into lamellipodium (front) and cell body (rear) reflecting underlying cytoskeletal "polarization." Distinct cytoskeletal mechanisms underlie the protrusion of the lamellipodium and the retraction of the trailing end of migrating cells (for review, see
Whereas the role of the cytoskeleton in cell migration has been studied in great detail, limited information is available on the role of ion transporters and ion channels in cell migration and on their distribution in crawling cells. In neutrophil granulocytes, chemotaxis is regulated by activation of the Na+/H+ exchanger (NHE)1 (
Previously, we studied the role of a Ca2+-sensitive K+ channel for migration of transformed renal epithelial (Madin-Darby canine kidney, MDCK-F) cells (
In addition, we studied the distribution of NHE and anion exchanger in migrating cells. Prompted by our own observation of polarized K+ channel activity (
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cell Culture
Experiments were carried out on alkali-transformed MDCK-F cells (
Migration Experiments
Migration of individual MDCK-F cells and human melanoma cells was monitored in paired experiments with video microscopy as described previously (
Local Superfusion Experiments
Migration experiments with local superfusion of either cell body or lamellipodium were performed as described previously (
Measurements of pHi
pHi of MDCK-F cells was measured by using video imaging techniques and the fluorescent pH indicator BCECF (Molecular Probes, Inc.). For dye-loading, MDCK-F cells were incubated in culture medium containing 2 µmol/liter BCECF-AM for 12 min. Coverslips were placed on the stage of an inverted microscope (Axiovert TV 100; Carl Zeiss, Inc.) and continuously superfused with prewarmed (37°C) Ringer's solution. Excitation wavelength alternated between 488 and 460 nm, respectively. The emitted fluorescence was monitored at 500 nm with an ICCD camera (Atto Instruments). Filter change and data acquisition were controlled by Attofluor software (Atto Instruments). Average fluorescence intensities (corrected for background fluorescence) were measured at 10-s intervals in several demarcated regions of interest placed over the projected cell surface.
At the end of each experiment, pHi measurements were calibrated by superfusing MDCK-F cells with a modified Ringer solution containing (mmol/liter): 125 KCl, 1 MgCl2, 1 CaCl2, 20 HEPES, and 10 µmol/liter nigericin using either two-point calibrations (pH 7.5 and 6.5) or four-point calibrations (pH 8.0, 7.5, 6.5, and 6.0).
The intracellular buffer capacity, ß, was determined by a modification of the method described by
Cell Volume Measurements
The effect of propionate on the volume of freshly trypsinized, suspended MDCK-F cells was determined electronically with a Coulter Counter. To obtain maximal propionate-induced swelling, we adopted a protocol described previously (
Immunofluorescence
MDCK-F cells growing on glass cover slips were rinsed twice with prewarmed PBS and fixed for 30 min with 3% paraformaldehyde in PBS. Fixed cells were washed with PBS, pH 7.4, PBS supplemented with 1% SDS (
Statistics
All data are presented as mean ± SEM. Paired or unpaired Student's t test were performed where applicable. Significance was assumed when P < 0.05.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
NHE Modulates Migration and pHi
MDCK-F cells migrate at a rate of 0.92 ± 0.02 µm/min (n = 320) under control conditions. The specific NHE blocker EIPA (100 nmol/liter25 µmol/liter) reduces the rate of migration to 52.0 ± 7.3% of control (Fig 1 A) in a dose-dependent manner. 25 µmol/liter EIPA elicits indistinguishable inhibition of migration when MDCK-F cells are superfused with CO2 /HCO3--buffered Ringer solution (48.2 ± 5.8% of control; n = 13; data not shown). Another specific NHE blocker, Hoe 694, has a similar effect. 1 and 10 µmol/liter Hoe 694 reduce the rate of migration to 76.9 ± 7.7% (n = 20) and 63.2 ± 5.6% of control (n = 18), respectively. Together, these data suggest a requirement for NHE activity for normal migration of MDCK-F cells. The half maximal inhibition in the low micromolar range points to the involvement of NHE1 (
|
As shown in Fig 1 B, NHE blockade with EIPA or Hoe694 is followed by a dose-dependent reduction of pHi from the control value of 7.28 ± 0.01 (n = 91). There is no detectable standing gradient of pHi between cell body and lamellipodium. Both NHE inhibitors reduce pHi to similar extents. Half maximal intracellular acidification and half-maximal inhibition of migration exhibit similar IC50 values, consistent with the involvement of the same NHE isoform in both processes. However, careful inspection of Fig 1A and Fig B, reveals subtle differences between the inhibition of migration by EIPA and the decrease of pHi. Whereas 1 µmol/liter EIPA has no effect on migration, it reduces pH i by 0.1 pH units. This suggests that moderate intracellular acidification does not suffice to inhibit cell migration, and that the Na +/H+ exchanger may modulate migration by mechanisms other than its impact on pHi. Nonetheless, these experiments are consistent with inhibition of migration by EIPA or Hoe694, reflecting blockade of the Na+/H+ exchanger.
Migration of MDCK-F Cells Depends on NHE Activity Rather than on pH i
If inhibition of migration due to NHE blockade is due to the reduction of pHi below a threshold of 0.1 pH units acidification, this effect should be mimicked by acidifying MDCK-F cells with weak organic acids such as propionic and formic acid. Their protonated forms permeate the cell and rapidly dissociate (
|
As shown in Fig 2 B, the marked acidification of MDCK-F cells with Na-propionate or with Na-formate does not inhibit migration. To test whether propionate-induced activation of NHE is responsible for the pH insensitivity of MDCK-F cell migration, we applied 15 mmol/liter Na-propionate in the presence of 10 µmol/liter EIPA. Under these conditions, migration is inhibited to the same extent as with EIPA alone (51.7 ± 7.6% of control; Fig 2 B).
Fig 3 plots the migration of MDCK-F cells as a function of the decrease of pHi. It is apparent that migration of MDCK-F cells does not solely depend on pHi, but rather on NHE activity per se. We made a qualitatively similar observation in ABP280-transfected melanoma cells. Whereas NHE blockade with EIPA almost completely inhibits migration (16.4 ± 5.9% of control), melanoma cells are slowed down only to 54.8 ± 14.5% of control rates (n = 14) in the presence of 15 mmol/liter propionate ( Fig 2 B). These observations raise the possibility that NHE activity may modulate migration due to its effect on cell volume. That increased NHE activity in the presence of propionate or formate is not followed by a stimulation of migration is probably due to the potentially inhibitory effect of lowered pHi on migration. However, this negative effect can be compensated for by increased NHE activity in MDCK-F cells.
|
Anion Exchange Is Required for Migration
Removal of extracellular Cl- in CO2/HCO3 --buffered Ringer's solution (isosmotically replaced by gluconate) demonstrates the existence of an anion exchanger in MDCK-F cells. Fig 4 A reveals that pHi immediately rises at a rate of 0.11 ± 0.01 pH units/min upon removal of Cl- (n = 36) and returns to baseline upon readdition of Cl- to the bath. The pH recovery upon addition of Cl- is sensitive to the anion exchange inhibitor, DIDS. Anion exchange activity is also evident in HEPES-buffered Ringer's solution. pHi rises at a rate of 0.06 + 0.01 pH units/min (n = 8) upon removal of extracellular Cl- (data not shown). Taking the intracellular buffering power into account, which is lower in the absence of CO2/HCO3 -, this corresponds to an approximately 10-fold lower transport rate of the anion exchanger than in the presence of exogenous CO 2/HCO3-.
|
As summarized in Fig 4 B, DIDS slows migration of MDCK-F cells in a dose-dependent manner. 100 and 500 µmol/liter DIDS almost completely inhibit migration of MDCK-F cells (22.3 ± 7.7% and 12.5 ± 5.7% of control, respectively). The sensitivity to DIDS is enhanced in the absence of exogenous CO2 /HCO3-. 25 µmol/liter DIDS elicit an almost complete inhibition of migration in HEPES-buffered Ringer's solution (20.7 ± 7.2% of control; Fig 4 C). This is consistent with the lower anion exchange activity in the absence of exogenous CO2/HCO3- being a rate-limiting step for normal cell locomotion. To test for the contribution of endogenously produced HCO3-, we also studied the effect of 100 µmol/liter acetazolamide, an inhibitor of carbonic anhydrase. Acetazolamide has no effect on migration by itself (104.7 ± 11.8% of control), nor does it accentuate the inhibition caused by 25 µmol DIDS in HEPES-buffered Ringer's solution (16.8 ± 5% of control; Fig 4 C). DNDS (100 µmol/liter), another inhibitor of anion exchange, also slows MDCK-F cells to 68.3 ± 8.3% of control values (n = 11; data not shown). DIDS (100 µmol/liter) almost completely inhibits migration of human melanoma cells as well (24.8 ± 9.6%; n = 12; Fig 4 B, inset). Thus, parallel operation of NHE and anion exchangers appears to be required for efficient locomotion of both cell types tested.
NHE Activity in MDCK-F Cells
We next determined the transport rate of the Na+/H+ exchanger in MDCK-F cells. Monitoring changes of pHi after stepwise reduction of extracellular NH4+ allowed calculation of the intrinsic buffer capacity ß. In the physiological range of pHi, ß is ~5 mmol-1 pH unit -1 (data not shown). NHE-mediated Na+ flux was calculated by multiplying ß by the initial change of pH (dpH/ dt) after application of EIPA or after removal of extracellular Na+ (0.03 pH units/min). Under basal "resting" conditions (pHi between 7.2 and 7.3), with the assumption of 1:1 Na+/H+ transport stoichiometry, NHE mediates uptake of 1.5 mmol/liter Na+ per min, corresponding to ~1% of the total cellular cation content per min.
NHE activity in MDCK-F cells was also measured as Na+ -dependent pHi recovery from imposed acid load. After acidifying cells in Na+-free Ringer's solution by removal of extracellular NH4+, readdition of extracellular Na+ initiated pHi recovery at a rate of 0.28 ± 0.03 pH units/min (n = 23; data not shown).
Local Superfusion Experiments
To contribute to cell migration, cell volume regulation should optimally be polarized within the cell. This hypothesis should be reflected by polarized distribution of volume regulatory ion transporters in the migrating cell. Therefore, we functionally tested the distribution of NHE and anion exchange activity in MDCK-F cells with a local superfusion technique (
Fig 5 summarizes the experiments with local superfusion of NHE inhibitors. When the lamellipodium is superfused with 25 µmol/liter EIPA, cells are slowed to the same extent as with superfusion of EIPA over the entire cell (50.5 ± 4.2% of control; n = 11). In contrast, when the cell body of migrating MDCK-F cells is exposed to EIPA, locomotion is not affected and cells move normally (103.4 ± 7.9% of control; n = 10; Fig 5 A). Hoe 694 (50 µmol/liter) has the same differential effect as EIPA when consecutively superfused over both cell poles of one cell. As shown in Fig 5 B, Hoe 694 slows migration only when applied to the lamellipodium of MDCK-F cells (41.2 ± 8.9% of control; n = 6), while it does not impair migration when directed to the cell body of the same cell (105.3 ± 4.2% of control; n = 6).
|
We next investigated whether the anion exchanger is also unevenly distributed in migrating MDCK-F cells by local superfusion of DIDS (25 µmol/liter) in CO2/HCO3- -buffered Ringer's solution (Fig 6 ). When DIDS is applied to the lamellipodium of migrating MDCK-F cells, they are slowed to 48.6 ± 6.4% of control. This degree of inhibition is identical to that produced by application of DIDS to the entire cell (compare with Fig 4 B). In contrast, when the cell body is exposed to DIDS, migration of MDCK-F cells is not impaired. MDCK-F cells move at the same rate (85.3 ± 5.8% of control; n = 9) of migration as when the cell body is superfused with control Ringer's solution. Taken together, these experiments suggest that functionally important NHE and anion exchangers are concentrated at the leading edge of migrating MDCK-F cells.
|
Immunocytochemical Localization of AE2 Anion Exchanger in Crawling Cells
As a correlate of the functional data on the localization of the anion exchanger, we visualized its distribution in MDCK-F cells with an antiAE2 antibody (
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We combined migration experiments with measurements of pHi and indirect immunofluorescence to study the functional roles of NHE and anion exchanger in cell migration. Our experiments clearly show that both transport activities are required for efficient locomotion of transformed renal epithelial cells and of human melanoma cells. NHE dependence of locomotion is also known for other cell types such as granulocytes (
NHE and anion exchanger are both involved in regulation of intracellular pH and cell volume homeostasis, both of which have been shown independently and in different cell types to be important for cell migration (
How can changing cell volume modulate migration? In our view, the distribution of NHE and anion exchanger points to a possible explanation. They are both localized at the leading edge of the lamellipodium. One of the mechanisms involved in the protrusion of the lamellipodium is gel-osmotic water flow into migrating cells at their leading edge (
By measuring cell volume of MDCK-F cells with the atomic force microscope, we provided indirect support for the idea of localized osmotic swelling at the leading edge of migrating cells. The volume of lamellipodium and cell body can change independently from each other since activating or inhibiting a Ca2+-sensitive K+ channel exclusively affects the volume of the cell body (
It is notable that NHE blockade inhibits migration to the same degree whether in HEPES buffer or in CO2/HCO3- -buffered Ringer's solution. The absence of exogenous HCO3 - might be expected to inhibit anion (Cl -/HCO3-) exchange in a HEPES-buffered solution and diminish the impact of NHE activity on cell volume. Intracellular HCO3- production appears not to drive Cl-/HCO3- exchange activity since blockade of carbonic anhydrase with 100 µmol/liter acetazolamide has no effect on cell migration in nominally CO2/HCO3--free solutions and since it does not pronounce the inhibitory effect of DIDS in HEPES-buffered Ringer's solution. However, we showed that the anion exchanger in MDCK-F cells also accepts OH- ions as counterions, although at an ~10-fold lower transport rate than its Cl- /HCO3- exchange rate. A similar observation was made for recombinant AE2 Cl-/HCO3 - exchanger, which can also function at ambient CO 2 conditions (
While we think that local regulation of cell volume is of major importance for the effect of NHE and anion exchanger on migration, we do not know the exact molecular mechanism by which these transporters elicit their action. Presently, we cannot rule out the possible involvement of changes in pHi. In amoeba, bundling and cross linking of actin filaments by elongation factor 1 is increased when pHi falls (
NHE1 is concentrated at sites of focal contact (
![]() |
Footnotes |
---|
Drs. Klein and Seeger contributed equally to this work and should be considered co-first authors.
1 Abbreviations used in this paper: DIDS, 4,4'-diisothiocyanate-stilbene-2,2'-disulfonic acid; EIPA, ethylisopropylamiloride; MDCK-F cells, Madin-Darby canine kidney cells; NHE, Na+/H+ exchanger.
![]() |
Acknowledgements |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We thank Dr. J. Reinhardt for help with confocal microscopy, and Drs. M. Gekle, H. Oberleithner, and S. Silbernagl for fruitful discussions during the course of the experiments. We thank Dr. H.-J. Lang (Hoechst AG) for providing us with EIPA, Hoe 694, and bumetanide.
This work was supported by Deutsche Forschungsgemeinschaft (SFB 176 A6) and by the National Institute of Diabetes and Digestive and Kidney Diseases (43495) and the Harvard Digestive Disease Center. S.L. Alper is an Established Investigator of the American Heart Association. Portions of this study were done by Magnus Klein and Ponke Seeger in partial fulfillment of the requirements for their Medical Degree.
Submitted: 29 December 1999
Revised: 13 March 2000
Accepted: 20 March 2000
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Boron, W.F. 1983 . Transport of H+ and ionic weak acids and bases. J. Membr. Biol. 72:1-16 [Medline].
Brown, D. , Lydon, J. , McLaughlin, M. , Stuart-Tilley, A. , Tyszkowski, R. , Alper, S. 1996 . Antigen retrieval in cryostat tissue sections and cultured cells by treatment with sodium dodecyl sulfate (SDS). Histochem. Cell Biol. 105:261-267 [Medline].
Condeelis, J. 1993 . Life at the leading edge: the formation of cell protrusions . Annu. Rev. Cell Biol. 9:411-444 .
Cunningham, C.C. , Gorlin, J.B. , Kwiatkowski, D.J. , Hartwig, J.H. , Janmey, P.A. , Byers, H.R. , Stossel, T.P. 1992 . Actin-binding protein requirement for cortical stability and efficient locomotion. Science 255:325-327 [Medline].
Edmonds, B.T. , Murray, J. , Condeelis, J. 1995 . pH regulation of the F-actin binding properties of Dyctyostelium elongation factor 1. J. Biol. Chem. 270:15222-15230
Grinstein, S. , Woodside, M. , Waddell, T.K. , Downey, G.P. , Orlowski, J. , Pouyssegur, J. , Wong, D.C.P. , Foskett, J.K. 1993 . Focal localization of the NHE-1 isoform of the Na+/H + antiport: assessment of effects on intracellular pH . EMBO (Eur. Mol. Biol. Organ.) J. 12:5209-5218 [Abstract].
Grinstein, S. , Goetz, J.D. , Furuya, W. , Rothstein, A. , Gelfand, E.W. 1984 . Amiloride-sensitive Na+H+ exchange in platelets and leukocytes: detection by electronic cell sizing. Am. J. Physiol. Cell Physiol. 247:C293-C298 [Abstract].
Hallows, K.R. , Packman, C.H. , Knauf, P.A. 1991 . Acute cell volume changes in anisotonic media affect F-actin content of HL-60 cells. Am. J. Physiol. Cell Physiol. 261:C1154-C1161
Ito, T. , Suzuki, A. , Stossel, T.P. 1992 . Regulation of water flow by actin-binding protein-induced actin gelation. Biophys. J. 61:1301-1305 [Abstract].
Jiang, L. , Chernova, M.N. , Alper, S.L. 1997 . Secondary regulatory volume increase conferred on Xenopus oocytes by expression of AE2 anion exchanger. Am. J. Physiol. Cell Physiol. 272:C191-C202
Jiang, L. , Stuart-Tilley, A. , Parkash, J. , Alper, S.L. 1994 . pHi and serum regulate AE2-mediated Cl- /HCO3- exchange in CHOP cells of defined transfection status. Am. J. Physiol. Cell Physiol. 267:C845-C856
Jöns, T. , Drenckhahn, D. 1998 . Anion exchanger 2 (AE2) binds to erythrocyte ankyrin and is colocalized with ankyrin along the basolateral plasma membrane of human gastric parietal cells. Eur. J. Cell Biol. 75:232-236 [Medline].
Lang, F. , Busch, G.L. , Ritter, M. , Völkl, H. , Waldegger, S. , Gulbins, E. , Häussinger, D. 1998 . Functional significance of cell volume regulatory mechanisms. Physiol. Rev. 78:247-306
Lauffenburger, D.A. , Horwitz, A.F. 1996 . Cell migration: a physically integrated molecular process. Cell. 84:359-369 [Medline].
Mackay, D. , Esch, F. , Furthmayr, H. , Hall, A. 1997 . Rho- and rac-dependent assembly of focal adhesion complexes and actin filaments in permeabilized fibroblasts: an essential role for ezrin/radixin/moesin proteins. J. Cell Biol. 138:927-938
Martin, M. , Roy, C. , Montcourrier, P. , Sahuquet, A. , Mangeat, P. 1997 . Three determinants in ezrin are responsible for cell extension activity. Mol. Biol. Cell. 8:1543-1557 [Abstract].
Mitchison, T.J. , Cramer, L.P. 1996 . Actin-based cell motility and cell locomotion. Cell. 84:371-379 [Medline].
Morgans, C.W. , Kopito, R.R. 1993 . Association of the brain anion exchanger, AE3, with the repeat domain of ankyrin. J. Cell Sci. 105:1137-1142
Murthy, A. , Gonzalez-Agosti, C. , Cordero, E. , Pinney, D. , Candia, C. , Solomon, F. , Gusella, J. , Ramesh, V. 1998 . NHE-RF, a regulatory cofactor for Na+/H+ exchange, is a common interactor for merlin and ERM (MERM) proteins . J. Biol. Chem. 273:1273-1276
Noel, J. , Pouyssegur, J. 1995 . Hormonal regulation, pharmacology, and membrane sorting of vertebrate Na+/H+ exchanger isoforms. Am. J. Physiol. Cell Physiol. 268:C283-C296
Oberleithner, H. , Westphale, H.-J. , Gaßner, B. 1991 . Alkaline stress transforms Madin-Darby canine kidney cells. Pflügers Arch. 419:418-420 .
Oster, G.F. , Perelson, A.S. 1987 . The physics of cell motility. J. Cell Sci. Suppl. 8:35-54 [Medline].
Plopper, G.E. , McNamee, H.P. , Dike, I.E. , Bojanowski, K. , Ingber, D.E. 1995 . Convergence of integrin and growth factor receptor signalling pathways within the focal adhesion complex. Mol. Biol. Cell. 6:1349-1365 [Abstract].
Reinhardt, J. , Golenhofen, N. , Pongs, O. , Oberleithner, H. , Schwab, A. 1998 . Migrating transformed MDCK cells are able to structurally polarize a voltage-activated K+ channel. Proc. Natl. Acad. Sci. USA. 95:5378-5382
Ritter, M. , Schratzberger, P. , Rossmann, H. , Wöll, E. , Seiler, K. , Seidler, U. , Reinisch, U. , Kahler, C.M. , Zwierzina, H. , Lang, H.-J. et al. 1998 . Effect of inhibitors of Na+/H+ exchange and gastric H+/K+ ATPase on cell volume, intracellular pH and migration of human polymorphonuclear leukocytes. Br. J. Pharmacol. 124:627-638 [Abstract].
Rosengren, S. , Henson, P.M. , Worthen, G.S. 1994 . Migration-associated volume changes in neutrophils facilitate the migratory process in vitro. Am. J. Physiol. Cell Physiol. 267:C1623-C1632
Schneider, S.W. , Pagel, P. , Rotsch, C. , Danker, T. , Oberleithner, H. , Radmacher, M. , Schwab, A. 2000 . Volume dynamics in migrating epithelial cells imaged with atomic force microscopy. Pflügers Arch. 439:297-303 .
Schwab, A. , Reinhardt, J. , Seeger, P. , Schuricht, B. , Dartsch, P.C. 1999 . K+ channel activity modulates migration and the actin cytoskeleton of transformed renal epithelial cells by controlling cell volume. Pflügers Arch. 438:330-337 .
Schwab, A. , Finsterwalder, F. , Kersting, U. , Danker, T. , Oberleithner, H. 1997 . Intracellular Ca2+ distribution in migrating transformed renal epithelial cells. Pflügers Arch. 434:70-76 .
Schwab, A. , Gabriel, K. , Finsterwalder, F. , Folprecht, G. , Greger, R. , Kramer, A. , Oberleithner, H. 1995 . Polarized ion transport during migration of transformed Madin-Darby canine kidney cells. Pflügers Arch. 430:802-807 .
Schwab, A. , Wojnowski, L. , Gabriel, K. , Oberleithner, H. 1994 . Oscillating activity of a Ca2+-sensitive K+ channela prerequisite for migration of alkali-transformed Madin-Darby canine kidney (MDCK-F) cells. J. Clin. Invest. 93:1631-1636 [Medline].
Schwartz, M.A. , Lechene, C. , Ingber, D.E. 1991 . Insoluble fibronectin activates the Na/H antiporter by clustering and immobilizing integrin alpha5 beta 1, independent of cell shape. Proc. Natl. Acad. Sci. USA. 88:7849-7853 [Abstract].
Simchowitz, L. , Cragoe, E.J., Jr. 1986 . Regulation of human neutrophil chemotaxis by intracellular pH. J. Biol. Chem. 261:6492-6500
Stuart-Tilley, A. , Sardet, C. , Pouysségur, J. , Schwartz, M.A. , Brown, D. , Alper, S.L. 1994 . Immunolocalization of anion exchanger AE2 and cation exchanger NHE1 in distinct, adjacent cells of gastric mucosa. Am. J. Physiol. Cell Physiol. 266:C559-C568
Tonetti, M. , Budnick, M. , Niedermann, R. 1990 . Receptor-stimulated actin polymerization requires acidification in human PMNs. Biochim. Biophys. Acta. 1054:154-158 [Medline].
Van Duijn, B. , Inouye, K. 1991 . Regulation of movement speed by intracellular pH during Dictyostelium discoideum chemotaxis. Proc. Natl. Acad. Sci. USA. 88:4951-4955 [Abstract].
Vexler, Z.S. , Symons, M. , Barber, D.L. 1996 . Activation of Na+-H+ exchange is necessary for RhoA-induced stress fiber formation. J. Biol. Chem. 271:22281-22284
Weintraub, W.H. , Machen, T.E. 1989 . pH regulation in hepatoma cells: roles for Na-H exchange, Cl -HCO3 exchange, and Na-HCO3 cotransport. Am. J. Physiol. Gastrointest. Liver Physiol. 257 :G317-G327