Summary
The effect of Amiloride on several parameters of sodium transport was investigated on the isolated frog skin. Amiloride at a concentration of 10−4 M/l decreased the sodium concentration in the sodium transport pool from 8.9 meq/kg cell water to 3.7 meq/kg cell water. No effect was observed on the intracellular sodium which is exchangeable from the corium side. Short circuit current and unidirectional sodium influx were diminished to the same extent whilst the unidirectional sodium efflux was not affected. In contrast to the short circuit current, which reaches a new steady state value within seconds, the unidirectional sodium influx reaches its new steady state with a half-time of 3.3 min. From the difference in the time courses of the decreases of short circuit current and unidirectional sodium influx, an amount of sodium could be calculated which agreed well with the directly measured fall in the sodium transport pool.
The results provide further evidence for the concept that Amiloride inhibits the passive entrance of sodium into the sodium transport compartment, without influencing the transport capacity of the sodium pump.
Zusammenfassung
An der isolierten Froschhaut wurde der Effekt von Amilorid auf verschiedene Parameter des Natriumtransportes untersucht. Amilorid vermindert bei einer Konzentration von 10−4 M/l die Natriumkonzentration im Natriumtransportkompartment von 8,9 auf 3,7 meq/kg Zellwasser. Das von der Coriumseite her austauschbare Natrium zeigt dagegen keine Änderung.
Kurzschlußstrom und unidirektionaler Natriuminflux werden durch Amilorid um den gleichen Betrag vermindert, während der unidirektionale Natriumefflux unbeeinflußt bleibt. Im Gegensatz zum Kurzschlußstrom, der sich innerhalb von Sekunden auf einen neuen Steady-State-Wert einstellt, erreicht der unidirektionale Natriuminflux seinen neuen Steady-State-Wert mit einer Halbwertszeit von 3,3 min. Aus den unterschiedlichen Zeitverläufen von Kurzschlußstrom und unidirektionalem Natriuminflux errechnet sich eine aus dem cellulären Raum in das Corium transportiert Natriummenge, die mit der direkt gemessenen Abnahme des Natrium im Transportkompartment gut übereinstimmt.
Die Resultate geben einen weiteren Anhalt dafür, daß Amilorid den passiven Einstrom von Natrium in das Natriumtransportkompartment vermindert, ohne die Transportkapazität der Natriumpumpe zu beeinflussen.
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Dörge, A., Nagel, W. Effect of Amiloride on sodium transport in frog skin. Pflugers Arch. 321, 91–101 (1970). https://doi.org/10.1007/BF00586365
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DOI: https://doi.org/10.1007/BF00586365