G. Krumschnabel et al., ACUTE AND CHRONIC EFFECTS OF TEMPERATURE, AND OF NUTRITIONAL STATE, ON ION HOMEOSTASIS AND ENERGY-METABOLISM IN TELEOST HEPATOCYTES, Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 167(4), 1997, pp. 280-286
Short- and long-term effects of temperature on ion flux and energy tur
nover were studied in hepatocytes from thermally acclimated trout and
roach. In trout hepatocytes K+ efflux was insensitive towards acute ex
posure to low temperature but was downregulated during cold acclimatio
n of the fish so as to balance the uncompensated decreased K+(Rb+) upt
ake of the cells. In contrast, both K+(Rb+) uptake and K+ efflux of ro
ach hepatocytes were temperature sensitive in the short term. These ac
ute effects, however, were offset during cold acclimation by a near pe
rfect compensation of both fluxes leading to re-establishment of ion f
lux homeostasis at the original level. Our findings, based on a new me
thod 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 acu
te and chronic temperature change. By comparing hepatocytes from two g
roups of trout, one kept on a maintenance diet (ration I)! the other f
ed ad libitum (ration II), we discovered striking effects of nutrition
al state on the absolute levels as well as on the temperature relation
ships of K+ uptake and protein synthetic activity. Both of these funct
ions in the hepatocytes increased in the ration II fed as compared to
the ration I fed trouts, but the increase of protein synthetic activit
y was greater and more uniform at the three experimental temperatures
than that of KC uptake. Moreover, protein synthetic activity proved to
be considerably more temperature sensitive than K+ uptake and, in con
trast to the latter, showed a compensatory response after cold acclima
tion.