THE USE OF TETRAALKYLAMMONIUM ION-SENSITIVE ELECTRODES FOR THE LIPOSOME MARKER RELEASE ASSAY

A series of teraalkylammonium ion-sensitive electrodes was constructed with the aim of finding new ionic markers suitable for use in the permeability assay of liposomal membranes. The series comprised the tetramethyl-, tetraethyl-, tetrapropyl-, tetrabutyl-, and tetraamylammonium ion homologues, and they were compared with tetraphenylphosphonium and K+ ion-sensitive electrodes. Tetraalkylammonium ions with alkyl chain lengths shorter than that of a propyl group and octanol-water partition coefficients of less than 5 X 10(-2) did not significantly permeate liposomal membranes composed of egg phosphatidylcholine and were trapped stably in the inner liposomal aqueous phase. We selected the tetraethylammonium ion for further study and verified its validity for use as a marker by conducting an experiment to determine antibody and complement activities by measuring the immunoreaction-induced liposomal membrane permeability changes. In addition to being suitable for use in such a conventional permeability assay, the tetraalkylammonium ion-sensitive electrodes were used successfully to determine the sizes of channels formed in liposomal membranes.