Galactocerebroside mediated transmembrane Ca2+ signalling in U-87 MG cells: Possible involvement of phosphoinositides.

ABSTRACT

Antibody to galactocerebroside (anti-GalC) has been shown to evoke a Ca2+ response in cultured glioma U-87 MG cells. The rise in [Ca2+]i was due to release of Ca2+ from the intracellular stores and influx through the plasma membrane. The rise in [Ca2+]i was markedly inhibited by neomycin sulphate and phorbol dibutyrate suggesting the involvement of phosphoinositides in Ca2+ mobilization. The Ca2+ response induced by anti-GalC was rapidly desensitized and repeated addition of anti-GalC did not elevate the [Ca2+]i . Heterologous desensitization was observed with bradykinin and adenosine triphosphate. The intracellular Ca2+ store mobilized by anti-GalC appears to be the IP3 sensitive pool of endoplasmic reticulum. The influx of Ca2+ is mediated by a channel. The Ca2+ influx was also prevented by pretreatment of cells with neomycin sulphate or phorbol dibutyrate. We propose that galactocerebroside may be associated with phospholipase C or other proteins linked to the phosphoinositide pathway of transmembrane signalling and anti-GalC activates the breakdown of phosphoinositides and thus mobilizes Ca2+ in U-87 MG cells.