Effect of Intraluminal Amiloride on Na Transport in the Rat Proximal Tubule

Abstract

Amiloride (3,5-diamino-6-chloropyrazinoylguanidine) was found to inhibit the unidirectional flux of 22Na in perfused proximal tubules of rats when the drug was present in the blood (1). The drug did not inhibit the net water reabsorption, therefore, it apparently did not have an affect on the active reabsorption of sodium.Since amiloride has been found to be a potent inhibitor of sodium reabsorption in the amphibian bladder and skin (2, 3) and since it has been found by the same authors that the inhibition of sodium transport is about one thousand times higher when the drug is on the source than when it is on the sink site of the sodium transport, experiments were designed to test the effect of the drug when present in the luminal and not in the interstitial site of the tubule cell.Methods. Sprague-Dawley rats weighing about 200 g were anesthetized with Inactin (100 mg/kg body wt.) and then infused through the right jugular vein with Ringer's solution a t a rate of 30 ml/hr-kg. Using a modification of the microperfusion technique and apparatus of Sonnenberg and Deetjen (4), proximal tubules were perfused at a rate of 20 nanoliters per min.Two pumps were used, one contained a control solution (Ringer's with 22Na and 14Cinulin) and the other contained the same solution plus 1 P M amiloride. A selected proximal tubule was first perfused with the control solution for 30-40 rnin, and 2-4 samples were obtained during this period. Then the control pump was withdrawn and substituted by the "amiloride" pump. Perfusion was restarted at exactly the same location. The amiloride perfusion was administered for 45-60 min during which time 2-4 samples were obtained. The use of the 2 pumps was randomized with ref-erence to their use for control or for amiloride perfusions.Each of the tubules perfused in the control period and in the diuretic period was injected with a latex solution ( 5 ) for later tubule identification and measurement. Concentrations of l4C-inulin and 22Na were determined with a three channel liquid scintillation counter.Results. Figure 1, presents a plot of the concentration ratio of collected over perfused fluid [ (TF)/(IF)] of 14C-inulin and 22Na, versus time. In this selected experiment three perfusion periods are presented: control, amiloride, and recovery or return to control. The (TF) / (IF) values for inulin were definitely reduced by amiloride and increased slightly when the amiloride perfusate was substituted by the control. The (TF)/(IF) values for sodium were definitely increased by amiloride returning to low levels when a control perfusate was reinstated. Table I, presents compiled data from eight perfusions (8 rats). The values presented for 0.2 / \ r -Control Amiloride Control w -Ic------+l 1 I I I I o 20 40 60 80 loo Time [minutes) FIG. 1. Effect of amiloride on proximal tubular reabsorption of water and sodium. Open circles are the collected fluid to perfusate ratios ( [ TF]/ [IF] ) of inulin concentration; dots are the same ratios for Na. Zero time refers to the beginning of the tubular perfusi...

Effect of amiloride on sodium and water reabsorption in the rabbit gall‐bladder.

“…Amiloride administered intravenously in diuretic doses exerts its effects on the distal part of the nephron without any effect on proximal tubular isosmotic salt and water reabsorption (Duarte, Chomety & Giebisch, 1971;Wilczewski, Olson & Carrasquer, 1974). Attempts to disclose an effect on fluid reabsorption of high concentrations of amiloride (10-4 to 1O-3 M) from the luminal side of proximal tubules in rats, using split oil-drop or microperfusion techniques (Carrasquer, Fravert & Olson, 1974;Meng, 1975), led to inconsistent results possibly due to the numerous sources of errors with both methods (Gottschalk & Lasssiter, 1973). During free-flow perfusion of rat proximal tubules Fromter & Gessner (1975) were unable to detect any effects of luminal 1O-3 M-amiloride on transepithelial potential and resistance; this was interpreted as a lack of effect of amiloride on net ion movements and paracellular conductance.…”

Change in Antikaliuretic Response to Potassium‐Sparing Diuretics in Patients with Cirrhotic Ascites

“…Unpredictable potassium excretion may be caused by the individually variable influence of the same dose of the same drug on the different nephron segments (15). Although the distal tubules are the “classic” site of action of PSD‐s, on the proximal tubules (20, 24, 25), Henle's loops (13, 14) and collecting ducts (14) have also been proposed.…”