The effect of poly-l-lysine,amiloride and methyl-l-lysine on gill ion transport and permeability in the rainbow trout

Summary The action of poly-l-lysine (PLL) on Na and Cl transport across freshwater fish gills was studied. Low concentrations (10^–6M) were added to the external medium for brief periods (1–5 min), then removed. During the next 20 min there was a rapid net loss of Na (117±17 Equiv100 g]^–1 hr^–1) and Cl (129±17 Equiv100 g]^–1 hr^–1). Both values are an order of magnitude larger than unidirectional effluxes in control fish. The efflux of both ions decreased to control values within 60 min after application and removal of PLL. In contrast, unidirectional influxes (J _in ^Cl andJ _in ^Na ) were inhibited by about 40% and showed no sign of returning to the original rates for 3 hr. Thus, PLL has two independent actions, causing a large increase in gill permeability which is reversible within an hour and a partial inhibition of influx which showed no sign of reversing for 2–3 hr. When PLL was applied for a longer period (60 min, the results were qualitatively similar but the permeability change was larger and persisted longer. These effects were compared with those of the small organic amines, amiloride and methyl-l-lysine. The latter inhibitedJ _in ^Na , but there was no other similarity to PLL. Neither affected sodium efflux, nor did they have any effect on Cl movements, in or out, across the gill. Inhibition ofJ _in ^Na , was rapidly and completely reversible, amd amiloride was shown to act by competing with Na for an entry site.