RESUMO
The effects of sodium pentobarbitone on the transepithelial potential difference and on the short-circuit current in the isolated toad skin were studied under different experimental conditions. Pentobarbitone was consistently effective when placed in the solution bathing the inside surface of the skin. The response to small concentrations (1.2, 3.6 and 6.0 x 10(-5) M) was a transient dose-related increase in the transepithelial potential difference and short-circuit current, and a decrease in both parameters at larger concentrations (3.6 x 10(-4) M). Total skin resistance decreased at small and increased at large concentrations. Analysis of the response in terms of the equivalent electrical circuit indicated that in small concentrations the effect was due to an increase in the driving force of the sodium (Na+) pump although the rate of entry of Na+ through the outer barrier was reduced. The activity of (Na+-K+)ATPase was increased within the first 7 min of the effect of pentobarbitone, thus confirming a direct action of the drug on Na+ transport. In large concentrations the electromotive force of the Na+ pump was decreased and inactivation of (Na+-K+)ATPase became evident. The effect of pentobarbitone was unchanged in six reserpinized toads, which would seem to rule out a catecholamine-mediated effect of the drug. The reduction of Na+-influx could indirectly increase transport efficiency since the rate of transport work should be reduced.