Ion selectivity and membrane potential effects of two scorpion pore-forming peptides
Parabutoporin (PP) and opistoporin 1 (OP1) are cation, a-helical antimicrobial peptides isolated from the southern African scorpion species, Parabuthus schlechteri and Opistophthalmus carinatus, respectively. Along with their antimicrobial action against bacteria and fungi, these peptides show pore-forming properties in the membranes of mammalian cells. Pore-formation and ion selectivity in cardiac myocytes were investigated by measuring the whole cell leak current by means of the patch clamp technique. Pore-formation was observed as the induction of leak currents. Ion selectivity of the pores was indicated by the shift of the reversal potential (Erev) upon substitution of intra (K⁺ with CS⁺ and CI- with aspartate) and extracellular (Na' with NMDG⁺) ions. Results were compared with the effect of gramicidin A used as a positive control for monovalent cation selective pores. PP and OP I induced a fluctuating leak current and indicate non-selectivity of PP and OP1-induced pores. An osmotic protection assay to determine estimated pore size was performed on the cardiac myocytes. PP and OP1-induced pores had an estimate pore size of 1.38-1.78 nm in diameter. The effect of PP and OP1 on the membrane potential (MP) of a neuroblastoma cell line and cardiac myocytes was investigated. TMRM was used to mark the MP fluorescently and a confocal microscope used to record the data digitally. The resting membrane potential (RMP) of the neuroblastoma cells was calculated at -38.3 f 1.9 mV. PP (0.5 μM) and OP1 (0.5-1 μM) depolarized the entire cell uniformly to a MP of -1 1.9 k 3.9 mV and -9.4 k 1.9 mV, respectively. This occurred after 20-30 min of peptide exposure. In the case of the cardiac myocytes depolarization was induced to -39.7 f 8.4 mV and -32.6 f 5.2 mV by 0.5-1 μM PP and 1.5-2.5 μM OPl, respectively.
- Health Sciences