Evidence for the modulation of cell calcium by epinephrine in fish hepatocytes.
The effect of epinephrine (10(-7) M) on cytosolic free-Ca2+ concentration ([Ca2+]i) and its dependency on external Ca2+ were studied in fura-2-loaded hepatocytes isolated from three teleost fish species: American eel, brown bullhead, and rainbow trout. Basal [Ca2+]i was similar in eel and trout hepatocytes (79.6 +/- 14.6 and 75.7 +/- 17.4 nM, respectively) but was significantly higher in bullhead cells (184 +/- 23 nM). Epinephrine-induced [Ca2+]i oscillations were observed only in eel hepatocytes. These oscillations, which presented variable patterns among individual cells, also developed in the absence of external Ca2+, although their amplitude progressively declined to eventually vanish under such conditions. In bullhead hepatocytes, epinephrine induced a biphasic [Ca2+]i response, with an initial transient rise followed by a sustained component; this response was virtually abolished in the absence of extracellular Ca2+. The peak [Ca2+]i achieved (433.5 +/- 135.6 nM) was more than two times that of eel cells (184.3 +/- 30 nM) but represented a similar percent increase above control [Ca2+]i for both species. Rainbow trout hepatocytes, contrary to eel and bullhead cells, demonstrated little epinephrine sensitivity, with less than 20% of the cells responding. These data clearly point to significant species differences both in terms of epinephrine-induced changes in [Ca2+]i and in the dependence of these transients on external Ca2+. Thus the eel response relies primarily on intracellular stores, whereas the bullhead response principally involves enhanced influx of Ca2+ from the extracellular milieu. Furthermore, the similarity of these responses with those reported for mammalian hepatocytes strongly suggests that an alpha-adrenoceptor/Ca2+ transduction system is involved in at least eel and bullhead hepatocytes.
Zhang
J
J
Department of Biology, Faculty of Medicine, University of Ottawa, Ontario, Canada.
Désilets
M
M
Moon
T W
TW
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004524:Eels / Q000378:metabolism*; D004837:Epinephrine / Q000494:pharmacology*; D007059:Ictaluridae / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D014337:Trout / Q000378:metabolism*
D002118:Calcium; D004837:Epinephrine