The effect of antidiuretic hormone on Na movement across frog skin

Abstract

SUMMARY1. The effect of antidiuretic hormone (ADH) on the movement and distribution of Na was studied. This was done using three different approaches: (a) the measurement of Na and 22Na in slices of epithelium of skins which were exposed to Ringer of varied composition containing 22Na, (b) the measurement of the influx of Na from the outer to the inner bathing solution with 22Na added to the outside, and (c) the use of a recently introduced technique which permits the direct evaluation of the flux from the outer solution -÷ epithelium, (JOT), i.e. the flux across the barrier which is generally regarded as the site of ADH activity.2. ADH increased the influx from the outer to the inner bathing solution of Na (50 %) not only when the concentration of Na on the outside was 115 mM (i.e. higher than in the epithelium) but even when the concentration was 1 mM (67 %).3. When the skin was bathed with 1mM-Na Ringer on the outside, ADH increased the unidirectional Na flux JOT by 56 % (Rana pipiens) and 71 % (Leptodactylus ocellatus). When the concentration was 115 mm a small increase (17 %) was observed in paired skins of R. pipiens. Under this condition no change was observed in L. ocellatus. 4. The amount of epithelial sodium which is labelled by 22Na added to the outside was taken to reflect the amount of Na involved in Na transport across the epithelium. Depending on whether the concentration of Na on the outside was high (115 mM) or low (1 mM), ADH produced an increase, or a decrease, of both the total Na content and the amount of 22Na exchanged.5. When the concentration of Na on the outside was low, ADH increased the total influx and JOT in spite of the fact that it lowers the total Na content and does not affect the exchangeable pool of Na. This observation is inconsistent with the view that the effect of ADH is due to the fact M. CEREIJIDO AND C. A. ROTUNNO that the increased permeability of the outer barrier allows more Na into the cell, and that the resulting increase of Na concentration in the cytoplasm accelerates the Na pumps at the inner side of the cells.6. It is concluded that ADH speeds up Na movements at the outward facing barrier, and that this exchange which facilitates the penetration of Na into a transporting compartment produces also a gain or a loss of Na in compartments not directly involved in Na transport across the epithelium. One compartment which is not involved in Na transport might be the cytoplasm of the epithelial cells.

Sodium uptake by frog skin and its modification by inhibitors of transepithelial sodium transport

“…The difficulty in detecting the inhibitory effects of amiloride when using high outside concentrations of sodium is in keeping with other findings where neither ouabain (Biber, 1971) nor antidiuretic hormone (Cereijido & Rotunno, 1971) can be shown to affect the uptake at high sodium concentrations though both change sodium uptake at low sodium concentrations. This could be due to problems associated with the correction for extracellular space, problems which make the quantification of an inhibitory response difficult.…”

Barriers to sodium movement across frog skin

“…The skin is then immersed into a thermos flask containing liquid nitrogen (--196 ~ The central part of the skin is cut into several transverse sections, each representing a certain uptake time of tracer. In previous papers (Rotunno et al, 1970;Cereijido & Rotunno, 1971) . After a period of preincubation in the desired Ringer's solution, the chambers are emptied.…”

Influx and efflux of sodium at the outer surface of frog skin

“…The frogs, Rana temporaria and Rana esculenta, were kept under running tap water at room temperature prior to the experiments. The arrangement used for measuring the uptake of Na from the epithelial side was similar to that described by Rotunno et aL [27] and Cereijido et al [9]. The isolated skin was mounted on a rectangular frame, exposing an area of 7.5 cm 2 (5 cm high and 1.5 cm wide) which was then inserted into a lucite Ussingtype chamber.…”