Previously we have reported that in glioma C6 cells, sphingosine stimulatory effect on phospholipase D (PLD) activity is independent of protein kinase C [Cell. Signal. 12 (2000) 399]. In this paper we have shown that this effect was also GTPgammaS independent and was completely inhibited by the plasma membrane methyl-beta-cyclodextrin cholesterol depletion what destroys caveolae structure. On the contrary, phorbol ester (12-O-tetradecanoylphorbol-13-acetate, TPA)-mediated PLD activity was enhanced by GTPgammaS and was only partially decreased by methyl-beta-cyclodextrin. We have also shown that TPA significantly increased expression of PLDla and PLDlb mRNAs and had lower effect on PLD2 mRNA. Sphingosine only slightly increased expression of PLD mRNA isoforms and did not cause synergistic effect when applied together with TPA. These results indicate that TPA, but not sphingosine, stimulates transcriptional activity of PLD isoforms. We also suggest that TPA stimulates primarily PLDI, while sphingosine affects PLD2 activity. This last process might occur at plasma membrane lipid microdomains. (C) 2004 Elsevier Inc. All rights reserved.