Abstract

The interaction of mice submandibular gland cells with LL-37 (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES), a cationic peptide with immunomodulatory properties, was investigated. LL-37 at a concentration that did not affect the integrity of the cells increased the uptake of calcium and activated a calcium-insensitive phospholipase A₂ (PLA₂). The small release of ATP induced by LL-37 could not account for this stimulation because apyrase did not significantly block the response to LL-37. The divalent cation magnesium inhibited the response to LL-37, but this inhibition was probably nonspecific because it also inhibited the in vitro bacteriostatic effect of the peptide. The increase of calcium uptake by LL-37 was not affected by 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-l-tyrosyl]-4-phenylpiperazine (KN-62), a rather specific inhibitor of P2X₇ receptors in mice. LL-37 also increased [Ca²⁺]_i in cells from mice invalidated for these receptors. LL-37 had no effect on the response to carbachol. It inhibited the increase of [Ca²⁺]_i and the activation of phospholipase D by ATP. It potentiated the activation of the PLA₂ by the nucleotide. Finally, LL-37 increased the fluidity of the plasma membrane of submandibular gland cells. In conclusion, our results suggest that LL-37 is an autocrine regulator of submandibular gland cells. It does not stimulate mouse P2X₇ receptors but modulates their responses.