Induction of cytosolic Ca²⁺ elevation mediated by Mas-7 occurs through membrane pore formation

Mas-7, a mastoparan derivative, induces elevation of intracellular free Ca²⁺ concentration ([Ca²⁺]_i) along two independent pathways. The minor contribution occurs via phospholipase C activation and is negatively regulated by treatment with phorbol 12-myristate 13-acetate, a protein kinase C activator. The major contribution involves plasma membrane pores allowing not only Ca²⁺, Mn²⁺, and Na⁺ to enter but also the uptake of ethidium bromide (314 Da) and lucifer yellow (457 Da), but not fura-2 (831 Da), Evans blue (961 Da), and fluorescein-conjugate phalloidin (1,175 Da). Mas-7-induced current, as measured in planar lipid bilayers, reveals that Mas-7-induced pores have two slope conductances, 290 and 94 pS, and that the pores are nonselective for cations. The results also indicate that Mas-7 can produce pores by direct interaction with the plasma membrane without the involvement of membrane proteins and cytosolic factors. Besides in human neuroblastoma cells, similar Mas-7 effects were also observed in other cell lines such as HL-60, 1321N1 human astrocytoma, and bovine chromaffin cells. The data suggest that the Mas-7-induced [Ca²⁺]_i elevation is the combined result of Ca²⁺ release from stores via phosphoinositide turnover and prolonged Ca²⁺ influx through membrane pores.