Cell shrinkage is essential in lysophosphatidic acid signaling in Ehrlich ascites tumor cells

The present study aimed at elucidating the initial intracellular lysophosph atidic acid (LPA)-induced signaling events, in order to investigate the seq uence in which LPA affects the intracellular concentration of free, cytosol ic Ca2+, [Ca2+](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 [Ca2+](i), which i s due to Ca2+ release from intracellular Ins(1,4,5)P-3-sensitive stores as well as an influx of Ca2+ The EC50 values for LPA-induced Ca2+ mobilization were estimated at 0.03 nM and 0.4 nM LPA in the presence and absence of ex tracellular Ca2+, respectively. The LPA-induced increase in [Ca2+](i) resul ted in (i) co-activation of Ca2+-activated, charybdotoxin (ChTX)sensitive K + and niflumic acid-sensitive Cl- currents; (ii) a subsequent cell shrinkag e and increased polymerization of F-actin, and (iii) activation of a Na+/H exchange, resulting in a concentration-dependent intracellular alkalinizat ion. The EC50 value for the LPA-induced rate of alkalinization was estimate d at 0.37 nM LPA. When cell shrinkage was prevented, the LPA-induced activa tion of the Na+/H+ exchanger was impaired. In conclusion, the initial signa ling events induced by LPA involves activation of volume regulatory mechani sms.