Characterization of Mas-7-induced Pore Formation in SK-N-BE(2)C Human Neuroblastoma Cells

Mastoparan, a peptide toxin from wasp venome, mimics receptors by stimulating the GTPase activity of guanine nucleotide binding proteins and the G-protein-coupled phospholipase C (PLC). By using Mas-7, the active analog of mastoparan, we showed that it makes pores in the plasma membrane. Treatment with Mas-7 but not Mas-17, the inactive analog, produced a concentration-dependent rise in intracellular Ca²⁺ concentration ([Ca²⁺]_i) and facilitated the uptake of ethidium bromide (EtBr) (314 Da) to a sustained level during the stimulation. In addition, Mas-7 triggered the influx of lucifer yellow (457 Da), while it did not induce the influx of fura-2 (831 Da) and Evans blue (961 Da). However, the Mas-7-induced permeability was selectively prevented by the addition of La³⁺, Ni²⁺, and Co²⁺, but not Cd²⁺. This blocking activity was concentration-dependent. While the stimulatory effect of Mas-7 on PLC activity was dependent on extracellular Ca²⁺, the pore forming activity of Mas-7 was not effected by removal of extracellular Ca²⁺. These results, therefore, suggest that the mastoparan's action in pore formation is independent from its action in PLC stimulation and is negatively effected by inorganic cations.