It is a well known fact that the isolated surviving frog skin, when in contact with Ringer solution on both dides, maintains for many hours a considerable potential difference between the inside and the outside, the inside being often more than 100 mV positive relative to the outside. I n previous papers the hypothesis was set forth that this potential difference was due mainly to an active and specific transport of Na ions inward, giving the inside solution a positive charge which in turn would attract C1 ions (and repel K ions), so t h a t the net result would be a transfer of XaC1 from the outside to the inside and to a lesser extent an exchange of outside Na against inside K. This view was based on the observation that the S a ion is the only ion so far studied which always moves from a lower to a higher electrochemical potential when the skin is alive and in contact with S a + containing solutions on both sides. This view has been strengthened recently by a study of the behaviour of the C1 ion in the isolated frog skin (KOEFOED JOHSSES, LEVI and USSING, 1951). It turned out that the C1 ion moves in an entirely passive way (compare CSSIKG, 1949 b) so that the electrochemical potential difference is the only force available for its transfer across the skin.However, even if the diffusion of C1 ions influences the skin POtential only in so far as it represents a short-circuit of the E. If. F. set up by the active transport of Na, the behaviour of the less abundant ions present in the system, notably those formed in the

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ZERAHN, K. Nature and localization of the sodium pool during active transport in the isolated frog skin. Acta physiol. scand. 1969. 77. 272-281.

Summary. The transport of lithium ions by the isolated surviving frog skin has been studied. By using the technique of short‐circuiting the skin it was first shown that the usual equality of net sodium transport and short‐circuit current was disturbed and, secondly, that this disturbance can be accounted for by the quantity of lithium which has passed through the skin plus the quantity which has accumulated in the skin. It was further demonstrated that lithium arid sodium compete on an equal basis in the transport process. Finally the ability of the frog skin to move lithium against an electrochemical gradient was shown, thus establishing the active nature of lithium transport.

ANDERSEN, B. and K. ZERAHN. Method f o r non-destructive determination of the sodium transport pool in frog skin with radiosodium. Acta physiol. scand. 1963. 59. [319][320][321][322][323][324][325][326][327][328][329]. -A method is described for measuring