Biochimica et Biophysica Acta, 693 (1982) 503-506 503 Elsevier Biomedical Press BBA Report BBA 70075 BRETYLIUM OPENS MUCOSAL AMILORIDE-SENSlTIVE SODIUM CHANNELS A. ILANI a, D. LICHTSTEIN a and M.B. BACANER b a Department of Physiology, Hebrew University-Hadassah Medical School Jerusalem (Israel) and b Department of Physiology, University of Minnesota, Minneapolis, MN (U.S.A.) (Received June 21st, 1982) Key words: Ion channek Bretylium; Amiloride," Na + channel," (Frog skin) Addition of the quanternary ammonium compound, bretylium, to the outer surface of a frog skin leads to an increase in the potential difference and in the short circuit current across the skin. Bretylium does not have any effect when applied to the inside face of the frog skin. The effect of bretylium is dependent upon the presence of sodium ions in the outer medium; it is depressed when sodium is replaced by choline or potassium but not when lithium substitutes for sodium. The bretylium effect is blocked by the specific sodium channel blocker, amiloride. It is proposed that bretylium opens mucosal, amiloride-sensitive sodium channels. Bretylium, a quanternary ammonium com- pound is known for its antifibriUatory activity in animals and humans [1,2]. Although extensively studied [1-4] the molecular mechanism responsi- ble for its pharmacological effect has not been established as yet. The compound is also known to stimulate and inhibit catecholamine release [5,6]. However, these effects are apparently not related to its antifibrillatory activity [6,7]. In the course of a study aimed at elucidating the mechanism of its action, we found that it has a specific action on the outer membrane of amphibian skins. We re- port here the main features of its action on this epithelium. Similar effects were observed on the toad bladder epithelium. Experiments were performed on the abdominal skin of Rana pipiens. Skins were held between two silicon rubber rings and the electrical membrane potential across the skin (pd) and membrane resis- tance were monitored using conventional tech- niques. (For more details see figure legends). Fig. 1 shows that bretylium tosylate when ap- plied to the outer surface of a frog skin causes a sustained reversible increase in the potential dif- ference across the skin. This increase in membrane 0005-2736/82/0000-0000/$02.75 © 1982 Elsevier Biomedical Press potential is accompanied by a small increase in conductance. The increase in potential difference is highly reproducible; of more than 50 trials of bretylium applications in the concentration range of 0.5 to 5 mM we never encountered a prepara- tion which failed to respond in a typical way. In 25 trials of application of 2.5 mM bretylium the percent increase in the potential difference across the skin was 45.6 + 2% (S.E.). The concomitant change in membrane conductance and in short circuit current was 18 + 2.3% and 78 + 5.8% (n = 9), respectively. A dose-response curve for a par- ticular preparation is shown in Fig. 2A. An ECs0 of approx. 1 mM can be estimated for the bretylium effect on the mucosal side of the epi- thelial cells. Bretylium has no effect on the poten- tial difference or on the conductance when applied to the inside face of the skin (Fig. 1). The following lines of evidence indicate that bretylium acts by increasing the permeability of the mucosal membranes to Na ÷ : (1) The effect of bretylium is depressed when sodium ions are re- placed by choline (Fig. 2B) or potassium ions (data not shown). On the other hand bretylium induces increase in potential difference and in