Effect of amiloride on catecholamine-induced changes in ion transport in short-circuited frog skin

The effect of amiloride (10(-6) M), added either before or after the catecholamine, on the adrenaline- or isoprenaline-induced changes in short-circuit current and Na and Cl fluxes of isolated skin of Rana temporaria was investigated. At the catecholamine concentration used the increment in short-circuit was the same in the absence or presence of amiloride (ca. 7.1 neq.cm-2.min-1) and the amiloride inhibition was the same in the absence or presence of catecholamine (ca. 9.4 neq.cm-2.min-1). Amiloride inhibited the Na and Cl influxes of the control period (by --8.63 +/- 1.28 and --2.08 +/- 0.75 neq.cm-2.min-1, respectively) but did not prevent the increase of these fluxes on the addition of adrenaline. There was no evidence of amiloride inhibition of the Na and Cl effluxes. There was an association between the increase of Na efflux and net Cl efflux following adrenaline, which if secreted together by a neutral NaCl pump would not contribute to the increased short-circuit current. The increased short-circuit current was correlated with the increased Na influx throughout the experiment if allowance is made for the periods where there is a lag between the current and isotopic measurement (i.e., the period immediately after the addition of a drug). It is tentatively suggested that the catecholamine-induced increase in Na influx is not altered by the amiloride concentration used in this study. In addition the magnitude of the changes induced by catecholamine in the influx and efflux of both Na and Cl seem to be unaffected.