Acute and chronic effects of temperature, and of nutritional state, on ion homeostasis and energy metabolism in teleost hepatocytes.
Short- and long-term effects of temperature on ion flux and energy turnover were studied in hepatocytes from thermally acclimated trout and roach. In trout hepatocytes K+ efflux was insensitive towards acute exposure to low temperature but was downregulated during cold acclimation of the fish so as to balance the uncompensated decreased K+ (Rb+) uptake of the cells. In contrast, both K+ (Rb+) uptake and K+ efflux of roach hepatocytes were temperature sensitive in the short term. These acute effects, however, were offset during cold acclimation by a near perfect compensation of both fluxes leading to re-establishment of ion flux homeostasis at the original level. Our findings, based on a new method permitting the simultaneous monitoring of K+ efflux and uptake in the same cell population, provide experimental verification of two of the three possible strategies, recently discussed by Cossins et al. (1995), by which the ionic steady state of fish cells may adjust to acute and chronic temperature change. By comparing hepatocytes from two groups of trout, one kept on a maintenance diet (ration I), the other fed ad libitum (ration II), we discovered striking effects of nutritional state on the absolute levels as well as on the temperature relationships of K+ uptake and protein synthetic activity. Both of these functions in the hepatocytes increased in the ration II fed as compared to the ration I fed trouts, but the increase of protein synthetic activity was greater and more uniform at the three experimental temperatures than that of K+ uptake. Moreover, protein synthetic activity proved to be considerably more temperature sensitive than K+ uptake and, in contrast to the latter, showed a compensatory response after cold acclimation.
Krumschnabel
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Abteilung für Okophysiologie, Universität Innsbruck, Austria.
Biasi
C
C
Schwarzbaum
P J
PJ
Wieser
W
W
D000064:Acclimatization / Q000187:drug effects / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000704:Analysis of Variance; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003530:Cyprinidae / Q000378:metabolism*; D006706:Homeostasis; D017136:Ion Transport; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011897:Random Allocation; D012413:Rubidium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000378:metabolism; D013696:Temperature
D015221:Potassium Channels; D011500:Protein Synthesis Inhibitors; D010042:Ouabain; D000255:Adenosine Triphosphate; D003513:Cycloheximide; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium