Differences in active sodium transport through frog skin with various experimental setups

Four experimental setups for examining active sodium transport by frog skin were examined and compared. They were: (I) a cannula, the interior of which faces the dermis; (II) a cannula, the interior of which faced the epidermis; (III) an Ussing-type chamber without gaskets; and (IV) an Ussing-type chamber with gaskets. The experiments were out in SO4-Ringer's solution. In control saline, the magnitude of the short circuit current (SCC microA/cm2) was in the order: I greater than III greater than II not equal to IV, while the magnitude of skin resistance (RM, k omega . cm2) and potential difference were: II not equal to IV greater than III greater than I. The responses of the skin to amiloride and cadmium varied greatly according to the various setups employed. Amiloride decreased the SCC and increased the RM. The percent differences from the control SCC and RM showed I not equal to IV greater than II and IV not equal to II greater than I, respectively. On the other hand, cadmium increased the SCC and decreased the RM. The orders of percent differences from the control SCC and RM were IV not equal to II greater than I and II not equal to IV greater than I. The effect of calcium gluconate on the active Na transport was also different depending on the various setups used; the responses to epidermal and dermal Ca-gluconate were quite opposite. The above seemingly curious findings are discussed in terms of the ENa, RNa, and R sigma obtained with Helman's Na-free saline method. From the present investigation, it is clear that careful attention should be given to the interpretation of experimental results in active transport studies when various kinds of setups are employed.