Evidence for the modulation of cell calcium by epinephrine in fish hepatocytes

Abstract

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.

Metabolic and endocrine functions of glucagon-like peptides — evolutionary and biochemical perspectives

“…Again, substantial species differences exist. Especially in the rainbow trout, only a low percentage of the cells observed gave positive Ca 2 + transients (Zhang et al 1992). In conclusion, a new look at GLP-dependent intracellular message transduction clearly seems warranted.…”

“…However, this view has recently been discounted by elegant experiments focussing directly on intracellular calcium. Using Fura-2 and spectrofluorimetry of isolated liver cells from three teleostean species, Moon and coworkers found at times sizeable Ca 2 + transients after application of physiological doses of epinephrine (Zhang et al 1992). Again, substantial species differences exist.…”

Adenylyl cyclase activity and glucose release from the liver of the European eel,Anguilla anguilla

“…However, the extent of glucose release does not appear proportional to AC activation, and it can be seen that glucose output is more stimulated in the catfish, whereas AC activity is more affected in the eel. As for the ␣ 1 -adrenergic transduction pathway, evidence that Ca 2ϩ and/or inositol trisphosphate (IP 3 ) intracellular changes trigger glucose output from the cells has not yet been found, notwithstanding extensive studies (12,13,15,45).…”

Carbohydrate metabolism and hepatic zonation in the Atlantic hagfish, Myxine glutinosa liver: effects of hormones

“…The existence of a classic mammalian a-and /-adrenoreceptor system in teleosts has been questioned (see Zhang et al 1992). Metabolically, the actions of phenylephrine, an a-agonist, can be blocked by a P-antagonist , although changes do occur in intracellular calcium (Zhang et al 1992).…”

“…Metabolically, the actions of phenylephrine, an a-agonist, can be blocked by a P-antagonist , although changes do occur in intracellular calcium (Zhang et al 1992). Adrenergic agonists and antagonists were used in hagfish hepatocytes to provide comparative information in an animal more primitive than a teleost.…”