Irreversible and reversible pore formation by polymeric alkylpyridinium salts (poly‐APS) from the sponge Reniera sarai

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Abstract
In this study, we investigated the electrophysiological actions of a high molecular weight fraction, predominantly containing two polymeric 1,3‐alkylpyridinium salts (poly‐APS) of 5.5 and ∼19 kDa isolated from the marine sponge Reniera sarai. The biological properties of poly‐APS are of particular interest because this preparation may be used to deliver macromolecules into the intracellular environment without producing long‐term damage to cells. Poly‐APS (50–0.05 μg ml−1) was applied to cultured dorsal root ganglion neurones or HEK 293 cells and changes in cell membrane properties were measured using whole‐cell patch‐clamp recording and fura‐2 Ca2+ imaging. Poly‐APS (50 μg ml−1) evoked irreversible depolarisations in membrane potential and reductions in input resistance. However, doses of 5 μg ml−1 and less produced reversible effects on these cell membrane characteristics and on Ca2+ permeability. At 0.05 μg ml−1, poly‐APS could robust transient increases in Ca2+ permeability without damaging the neurones or subsequently attenuating Ca2+ entry through voltage‐activated channels. Bathing cells in NaCl‐based extracellular medium containing 1.5 mM zinc attenuated the irreversible and reversible effects of poly‐APS on membrane properties (membrane potential, input resistance and whole‐cell currents). In both DRG neurones and HEK 293 cells, zinc attenuated Ca2+ entry evoked by poly‐APS. These effects of zinc were only observed if zinc was continually present during poly‐APS application. However, zinc failed to attenuate the actions of poly‐APS if it was applied after the sponge toxin preparation had evoked changes in membrane properties. In conclusion, the pore‐forming preparation poly‐APS can have dose‐dependent interactions with cell membranes and at low doses these can be reversible. Additionally, the interactions between poly‐APS and cell membranes could be attenuated by zinc. British Journal of Pharmacology (2003) 139, 1399–1408. doi:10.1038/sj.bjp.0705374