Salt‐induced changes in sodium transport across the skin of the euryhaline toad, Bufo viridis.

Abstract

SUMMARY1. Euryhaline toads (Bufo viridis) were adapted to either distilled water, 115 or 200 mm-NaCl solutions. Na transport across the skin of these animals was studied in in vitro preparations.2. Salinity adaptation caused a reduction in transepithelial potential and short-circuit current across the skin, and increased its electrical resistance.3. Na influx across the skin was decreased. The reduction accounted fairly well for the measured reduction in short-circuit current.4. Short-term Na uptake at the outer barrier of the skin was greatly reduced in preparations from salt adapted animals. Amiloride, which usually inhibits Na uptake, did not affect it in skins from salt adapted toads.5. Sodium conductance decreased by a factor of three in skins from 115 mM-NaCl adapted toads, and to zero in skins from 200 mM-NaCl adapted animals. Shunt conductance was only little affected by the salinity of adaptation.6. 'Amiloride-sensitive component' of transepithelial Na transport was 55, 21.5, and 4*5,uA/cm2 in skins from toads which were adapted to distilled water, 115, and 200 mm-NaCl solutions, respectively. 7. It is concluded that the effect of salinity adaptation on the skin of the toad is to reduce the number of Na selective sites at the outer barrier. This change is reflected in a decrease in the 'amiloride-sensitive component' of Na transport across the skin, and could not be increased by aldosterone. Other changes may occur as secondary to that.

Induction of transporting sites in a sodium transporting epithelium.

“…In yet another species, Bufo viridis, it has been reported that adaptation of these animals to high salinities results in a reduction of amiloride sensitive sodium transport and a reduction of mucosal sodium influx (Katz, 1975). The author concludes that the effect of saline adaptation is to 'reduce the number of Na selective sites at the outer barrier', a conclusion which is in accord with our direct measurements of site density.…”

“…A sodium transporting epithelium was deprived of sodium for a period of 1 week and at the end of this time the level of transport and the density of sodium entry sites in the epithelium were measured. It had already been established that adaptation of amphibian epithelia to high or low salinities influenced the subsequent level of sodium transport by a negative feed-back reaction, that is deprived tissues had elevated transport capability and vice versa (Bentley, 1973;Katz, 1975). In these experiments it was found that sodium deprivation increased both the level of sodium transport and the numbers of membrane macromolecules controlling sodium entry into the epithelium.…”

Sodium chloride transport across the chicken coprodeum. Basic characteristics and dependence on sodium chloride intake

“…However, judged from the change in net sodium transport the factor of adaptation appears to be above 100, and it can even be argued that adaptation to a high-sodium diet leads to a complete suppression of the rheogenic sodium transport. Even the lowest of these estimates of the ability ofthe chicken coprodeum to adapt functionally to the dietary sodium load exceeds the degree of adaptation observed for other sodium-transporting epithelia like rat colon and rectum (Edmonds, 1967), toad urinary bladder (Fanestil, Herman, Fimognari & Edelman, 1968), the skin of an euryhaline toad (Katz, 1975), and the goldfish intestine (Ellory, Lahlou & Smith, 1972). In the toad colon, how-501 502 I. CHOSHNIAK, B. G. MUNCK AND E. SKADHAUGE ever, the adaptation, although smaller in range, proceeds to a reversal of the sodium transport from net absorption to net secretion (Ferreira & Smith, 1968).…”

Osmoregulation of the cane toad, Bufo marinus, in salt water

“…Although a sodium pump is necessary for the survival of amphibians in fresh water a decrease in its activity when animals are in highly saline environments would place less burden on the kidneys and bladder to excrete excess electrolytes. A decrease in sodium uptake has been shown in several species when acclimated to high salinities (Ferreira and Jesus, 1973;Katz, 1975).…”