Effect of ouabain, amiloride, and antidiuretic hormone on the sodium-transport pool in isolated epithelia from frog skin (Rana temporaria).

When tracer Na+ is added to the solution bathing the apical side of isolated epithelia the observed transepithelial tracer influx increases with time until a steady state is reached. The build-up of the tracer flux follows a single exponential course. The halftime for this build-up under control conditions was 0.92 +/- 0.06 min, and in the presence of ouabain 4.51 +/- 0.7 min. It is shown that the calculated Na+-transport pool is located in the cells. The Na+-transport pool under control conditions was 35.6 +/- 3.4 nmol/cm2, which corresponds to an intracellular Na+ concentration of 7.9 mM. Activation of the active Na+ transport by addition of antidiuretic hormone resulted in a highly significant increase in the Na+ transport pool, and inhibition of the transcellular Na+ transport with amiloride resulted in a decrease in the Na+-transport pool. Furthermore, the active Na+ transport increased along an S-shaped curve with increasing intracellular Na+ concentration (Na+-transport pool). The Na+ pump was found to be half saturated at an intracellular Na+ concentration of 12.5 mM.