Cell shrinkage is essential in lysophosphatidic acid signaling in Ehrlich ascites tumor cells.
The present study aimed at elucidating the initial intracellular lysophosphatidic acid (LPA)-induced signaling events, in order to investigate the sequence in which LPA affects the intracellular concentration of free, cytosolic Ca(2+), [Ca(2+)](i), ion channels, the F-actin cytoskeleton, cell volume and the Na(+)/H(+) exchanger. We found that stimulation of Ehrlich cells with LPA induced a transient, concentration-dependent increase in [Ca(2+)](i), which is due to Ca(2+) release from intracellular Ins(1,4,5)P(3)-sensitive stores as well as an influx of Ca(2+). The EC(50) values for LPA-induced Ca(2+) mobilization were estimated at 0.03 nm and 0.4 nm LPA in the presence and absence of extracellular Ca(2+), respectively. The LPA-induced increase in [Ca(2+)](i) resulted in (i) co-activation of Ca(2+)-activated, charybdotoxin (ChTX)-sensitive K(+) and niflumic acid-sensitive Cl(-) currents; (ii) a subsequent cell shrinkage and increased polymerization of F-actin, and (iii) activation of a Na(+)/H(+) exchange, resulting in a concentration-dependent intracellular alkalinization. The EC(50) value for the LPA-induced rate of alkalinization was estimated at 0. 37 nm LPA. When cell shrinkage was prevented, the LPA-induced activation of the Na(+)/H(+) exchanger was impaired. In conclusion, the initial signaling events induced by LPA involves activation of volume regulatory mechanisms.
Pedersen
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S
August Krogh Institute, Department of Biochemistry, Universitetsparken 13, University of Copenhagen, DK-2100 Copenhagen O, Denmark.
Hoffmann
E K
EK
Hougaard
C
C
Lambert
I H
IH
D000199:Actins / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002286:Carcinoma, Ehrlich Tumor / Q000473:pathology / Q000503:physiopathology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D048429:Cell Size / Q000187:drug effects; D018999:Charybdotoxin / Q000494:pharmacology; D018118:Chloride Channels / Q000502:physiology; D002712:Chlorides / Q000378:metabolism; D003599:Cytoskeleton / Q000187:drug effects; D003600:Cytosol / Q000378:metabolism; D005260:Female; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008246:Lysophospholipids / Q000494:pharmacology*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D009544:Niflumic Acid / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012413:Rubidium / Q000493:pharmacokinetics; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects / Q000378:metabolism; D013654:Taurine / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000199:Actins; D018118:Chloride Channels; D002712:Chlorides; D008246:Lysophospholipids; D017923:Sodium-Hydrogen Exchangers; D018999:Charybdotoxin; D013654:Taurine; D009544:Niflumic Acid; D015544:Inositol 1,4,5-Trisphosphate; D012413:Rubidium; D011188:Potassium; D002118:Calcium