Non‐electrolyte permeability of trout gills: effect of temperature and adrenaline

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Abstract
1. The gill permeability to various non‐electrolytes (Ps) was measured in fresh‐water and sea‐water adapted trout (Salmo gairdneri). This study was performed in vitro using a ‘head‐perfused’ preparation. The influence of temperature and adrenaline (10−6 M) on permeability to non‐electrolytes was also investigated.2. During salt adaptation Pbutanol and Pwater decrease, Pmannitol rises and Pdextran stays constant. In view of recently acquired morphological data these results back up the hypothesis of different pathways across the gill epithelium (transcellular, vesicular and paracellular) according to the physico‐chemical characteristics of the molecules. The low selectivity of the gill epithelium as a function of the liposolubility of the molecules used testifies to the hydrophilic nature of diffusion across this epithelium, a feature becoming more pronounced during salt adaptation.3. The activation energies are about 4 kcal/mol, an energy comparable to diffusion in water for most of the substances tested, exceptions being butanol for fresh‐water adapted gills and water for fresh‐water and sea‐water adapted gills. Arrhenius plots for butanol in fresh water gills show a transition temperature at 15 °C, suggesting an increased membrane lipid fluidity above this temperature.4. Adrenaline has no effect on Pmannitol and Pdextran, but increases Pbutanol and Pwater selectively according to the adaptation medium (+ 160% and + 100% in fresh water and + 25% and + 20% in sea water respectively). These results point to an effect of this catecholamine on the membrane lipid fluidity.