Branchial sodium uptake was measured across secondary lamellae (SL) using the isolated-perfused head preparation. This study was correlated with histological examination.Freshwater trout, Sulmo guirdneri, were exposed to various artificial media:distilled water (DW), fresh water (FW: NaCl < 200 pMA; C a + + = 1.5 mMA), FW + 5 mM CaCl2 and FW + 10 mM CaC12. These environments altered the number and forms of "chloride cells" (CC) located in SL and were related to changes in maximal transport rate of Na+. An increase in a specific type of CC (round) was associated with a n increase in V, , , , and a decrease in round cells was associated with a decrease in V, , , .

No abstract

Effects of copper were studied in freshwater adapted rainbow trout using the perfused head preparation. In its monovalent chemical form, copper at millimolar concentrations had no significant effects on Na+ and water transport. By contrast, the divalent form produced an increase in gill perfusion pressure, a significant reduction in Na+ influx and water fluxes and reversed Na+ net flux. Observations by light microscopy showed important cell damage (oedema, mucus production, cellular desquamation). By electron microscopy there was smoothing of apical membranes, swelling of the tubular system and destruction of mitochondria. The Na, K-ATPase activity was totally suppressed and residual ATPase activity largely inhibited by 1 mM Cu2+. There was inhibition of the Na,K-ATPase activity with an IC50 of approximately 10 microM of total copper (free and bound cupric fractions). As active sodium transport is located on the secondary lamellae, our results show that its entry mechanism is inhibited at that level by cupric ions only. Results are discussed in relation to hydromineral balance of the trout.

The following study combines histological observations on the localization and density of mitochondria-rich cells with a kinetic study of the part played by these cells in transport phenomena. In the ventral skin, mitochondria-rich cells and granular cells are equally abundant in the first living cell layer. The mitochondria-rich cells were shown to excrete methylene blue [3,9-bis-(dimethylamino)-phenozathionum chloride]. A kinetic study of this excretion across the isolated epithelium of Rana esculenta skin showed that the mechanism of the excretion was a saturable one. An important fraction of methylene blue excretion depends on the absorption of sodium; the absence of this ion, or the inhibition of its transport by ouabain or amiloride, inhibits the excretion of the organic base. The mitochondria-rich cells, however, do not appear to play a determining role in sodium transport.

Urea influxes (Ji) and effluxes (Je) were studied across the isolated skins of Rana esculenta, Bufo bufo, and B. viridis. Two symmetrical pieces of the same skin, bathed in Ringer + 2 mM urea, were used for the two fluxes. In R. esculenta the urea fluxes are passive when the animals are kept in running water but become active after dehydration in air or preadaptation in saline solutions. The ratio Ji/Je can vary between 3 and 27 and the Ji between 2 and 22 nmol . h-1 . cm-2 according to preadaptation. Only the active fluxes obey saturation kinetics. Urea absorption is always independent of sodium transport. In toads, active urea transport occurs even when hydrated. It is markedly stimulated by saline preadaptation. A correlation between the degree of active urea transport across the skin and the capacity of the species to endure dehydrating conditions would appear to exist. The physiological significance of this transport mechanism is discussed.