Phosphoinositide hydrolysis in permeabilized SH-SY5Y human neuroblastoma cells is inhibited by mastoparan.

The effects of mastoparan on phospholipase C-catalysed phosphoinositide hydrolysis were examined in [3H]inositol-labelled human neuroblastoma SH-SY5Y cells. [3H]Inositol phosphate formation in intact cells was not altered by 20 microM mastoparan. In contrast, [3H]inositol phosphate formation in electrically permeabilized cells stimulated with guanosine 5'-[gamma-thio]triphosphate and/or carbachol was inhibited by mastoparan with half-maximal effects at approx. 3 microM. The peptide was much less effective in inhibiting stimulatory effects of Ca2+. Similar but less potent inhibitory effects were observed with the cations, neomycin and spermine, indicating that direct interaction of mastoparan with polyphosphoinositides might account for its inhibitory effects on inositol phosphate formation.