lab 23 - J . M embrane Biol., 13, 143-164 (1973) 9 b y...

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J. Membrane Biol., 13, 143-164 (1973) by Springer-Verlag New York Inc. 1973 Temperature-Dependent Changes in Fluid Transport across Goldfish Gallbladder D. Cremaschi *, M. W. Smith and F. B. P. Wooding A.R.C. Institute of Animal Physiology, Babraham, Cambridge, CB2 4AT, England Received 12 March 1973 Summary. The temperature dependence of fluid transport across in vitro preparations of goldfish gallbladder was measured using a gravimetric technique. Fluid transport showed a direct dependence on incubation temperature when the adaptation temperature was kept constant. For constant incubation temperature, transport fell as the adaptation temperature rose. The width of intercellular channels varied with incubation and adapta- tion temperature as expected if fluid were to cross the tissue by this route. The structure of the gallbladder was otherwise unaffected by changes of temperature. Intracellular concentrations of Na, K and C1 also depended on the environmental temperature of the fish. The levels of Na and C1 increased and the level of K decreased, at constant incubation temperature, as the adaptation temperature rose from 8 to 30 ~ These changes took two to three weeks to become apparent while fluid transport regulated within 20 hours of raising the environmental temperature. The osmotic permeability of the gallbladder remained independent of both incubation and adaptation temperature. The outcome of adaptation was to maintain constant both the ionic composition of the epithelium and the rate at which it could transport fluid, when these parameters were measured at incubation temperatures equal to the previous environmental tem- perature of the fish. The significance of these findings is discussed and a mechanism for regulation postulated which involves an initial regulation of salt entry into the rnucosa followed by long term changes in the pumping ability of newly synthesized cells. The mechanism whereby water is removed from bile held within the gallbladder is now understood in some detail, thanks largely to the work of Diamond and his co-workers (see the review of Diamond, 1968). The active extrusion of salt into intercellular channels creates a standing osmotic gradient which then provides the driving force for fluid movement (Kaye, Wheeler, Whitlock & Lane, 1966; Diamond & Bossert, 1967; Tormey & Diamond, 1967). Such a mechanism for fluid transport might be expected to be particularly susceptible to temperature and, indeed, changes in * Present address: Istituto di Fisiologia Generale, Universit/t degli Studi di Milano, Italy.
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144 D. Cremaschi, M. W. Smith and F. B. P. Wooding temperature have already been used successfully to provide morphological evidence of the temperature dependence of fluid transport, the extent to which intercellular channels remain open being shown to depend on the temperature at which gallbladders are incubated (Tormey & Diamond, 1967; Smulders, Tormey & Wright, 1972). This effect of temperature on transport has in most cases little physiological significance, since the temperature of the animal remains constant. This is not true for the goldfish
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lab 23 - J . M embrane Biol., 13, 143-164 (1973) 9 b y...

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