Transport of lithium and rectification by frog skin

The isolated frog skin, bathed with Li⁺-Ringer (Na⁺-free) on the outside and Na⁺-Ringer on the inside, can maintain a normal potential difference (PD) and short-circuit current (s.c.c.) for more than 6. h. The s.c.c. correspondended to the Li⁺ influx. The Na⁺ efflux was 4% of the s.c.c. 10⁻⁵ M ouabain depressed Li⁺ influx and s.c.c. 10¹⁰⁻⁵ M amiloride abolished the Li⁺ s.c.c., while 0.1 unit/ml oxytocin stimulated it. When the inside of the skin was bathed with Li⁺-Ringer, PD and s.c.c. fell to zero within 2 h. The oxygen consumption of skin slices bathed in Li⁺-Ringer was 29% lower than controls bathed in Na⁺-Ringer.When the isolated frog skin is bathed in Na₂SO₄-Ringer it shows electrical rectification which has been correlated with the active transport of Na⁺. In skins transporting Li⁺, rectification characteristics are similar to those of skins transporting Na⁺. When the inner face of the skin is bathed with Li⁺-Ringer, rectification, PD and s.c.c. decline in a parallel fashion.It is concluded that: (1) Li⁺ can be transported when Na⁺ is present at the inner face. (2) Amiloride, ouabain and oxytocin affect Li⁺ and Na⁺ transport in a similar manner. (3) Li⁺ transport, like Na⁺ transport, is associated with rectification. (4) Active transport of Na⁺ and Li⁺ seems to depend on two different but associated proceses; one taking place at the external barrier (where rectification occurs) as shown by the effect of amiloride; and the other of an inner site related to energy requirements and affected by ouabain and Li⁺. (5) The cation being transported is not necessarily activating the (Na⁺-K⁺-ATPase.