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

The action of poly-L-lysine (PLL) on Na and Cl transport across freshwater fish gills was studied. Low concentration (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 muEquiv[100 g]-1hr-1) and Cl (129+/17 muEquiv[100 g]-1hr-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 (JCl in and JNa in) 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 apartial 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 inhibited JNa in, but there was not other similarity to PLL. Neither affected sodium efflux, not did they have any effect on Cl movements, in or out, across the gill. Inhibition of JNa in, was rapidly and completely reversible, and amiloride was shown to act by competing with Na for an entry site.