scholarly journals The contribution of both extracellular and intracellular calcium to the action of α-adrenergic agonists in perfused rat liver

1984 ◽  
Vol 220 (1) ◽  
pp. 35-42 ◽  
Author(s):  
P H Reinhart ◽  
W M Taylor ◽  
F L Bygrave
Keyword(s):  
Rat Liver ◽  
Perfused Rat Liver ◽  
Adrenergic Agonists ◽  
Adrenergic Agonist ◽  
Redox Ratio ◽  
Lactate And Pyruvate ◽  
Body Production ◽  
Sustained Responses ◽  
Alpha Adrenergic Agonist

The role of both intracellular and extracellular Ca2+ pools in the expression of alpha-adrenergic-agonist-mediated responses was examined in perfused rat liver. Responses studied included glycogenolysis, respiration, lactate and pyruvate formation, ketone-body production, changes in the cytoplasmic and mitochondrial redox ratio and cellular K+ fluxes. Each of these was shown to be dependent on the mobilization of intracellular Ca2+ and can be grouped into one of two response types. Transient responses (ion fluxes and the redox ratios) are obligatorily dependent on the mobilization of intracellular Ca2+ and occur irrespective of the extracellular Ca2+ concentration. Sustained responses, on the other hand, initially require intracellular Ca2+ and, subsequently, extracellular Ca2+. The data indicate that alpha-adrenergic agonists mobilize extracellular Ca2+ as well as intracellular Ca2+ and that both pools are required for the full expression of hormone-induced responses in rat liver.

scholarly journals The action of α-adrenergic agonists on plasma-membrane calcium fluxes in perfused rat liver

1984 ◽  
Vol 220 (1) ◽  
pp. 43-50 ◽  
Author(s):  
P H Reinhart ◽  
W M Taylor ◽  
F L Bygrave
Keyword(s):  
Plasma Membrane ◽  
Rat Liver ◽  
Potential Role ◽  
Dependent Manner ◽  
Perfused Rat Liver ◽  
Adrenergic Agonists ◽  
Mediated Effects ◽  
Alpha Agonist ◽  
Alpha Adrenergic Agonist

The effect of alpha-adrenergic agonists on Ca2+ fluxes was examined in the perfused rat liver by using a combination of Ca2+-electrode and 45Ca2+-uptake techniques. We showed that net Ca2+ fluxes can be described by the activities of separate Ca2+-uptake and Ca2+-efflux components, and that alpha-adrenergic agonists modulate the activity of both components in a time-dependent manner. Under resting conditions, Ca2+-uptake and -efflux activities are balanced, resulting in Ca2+ cycling across the plasma membrane. The alpha-adrenergic agonists vasopressin and angiotensin, but not glucagon, stimulate the rate of both Ca2+ efflux and Ca2+ uptake. During the first 2-3 min of alpha-agonist administration the effect on the efflux component is the greater, the net effect being efflux of Ca2+ from the cell. After 3-4 min of phenylephrine treatment, net Ca2+ movements are essentially complete, however, the rate of Ca2+ cycling is significantly increased. After removal of the alpha-agonist a large stimulation of the rate of Ca2+ uptake leads to the net accumulation of Ca2+ by the cell. The potential role of these Ca2+ flux changes in the expression of alpha-adrenergic-agonist-mediated effects is discussed.

scholarly journals The Ca2+-mobilizing actions of vasopressin and angiotensin differ from those of the α-adrenergic agonist phenylephrine in the perfused rat liver

1985 ◽  
Vol 232 (3) ◽  
pp. 911-917 ◽  
Author(s):  
J G Altin ◽  
F L Bygrave
Keyword(s):  
Plasma Membrane ◽  
Rat Liver ◽  
Similar Amount ◽  
Perfused Rat Liver ◽  
Adrenergic Agonists ◽  
Adrenergic Agonist ◽  
Hormone Administration ◽  
Sensitive Electrode ◽  
Stimulation Of

A Ca2+-sensitive electrode was used to study net Ca2+-flux changes induced by the administration of phenylephrine, vasopressin and angiotensin to the perfused rat liver. The studies reveal that, although the Ca2+ responses induced by vasopressin and angiotensin are similar, they are quite different from the Ca2+ fluxes induced by phenylephrine. The administration of phenylephrine is accompanied by a stimulation of a net amount of Ca2+ efflux (140 nmol/g of liver). A re-uptake of a similar amount of Ca2+ occurs only after the hormone is removed. In contrast, the administration of vasopressin or angiotensin to livers perfused with 1.3 mM-Ca2+ induces the release of a relatively small amount of Ca2+ (approx. 40 nmol/g of liver) during the first 60 s. This is followed by a much larger amount of Ca2+ uptake (70-140 nmol/g of liver) after 1-2.5 min of hormone administration, and a slow efflux or loss of a similar amount of Ca2+ over a period of 6-8 min. At lower concentrations of perfusate Ca2+ (less than 600 microM) these hormones induce only a net efflux of the ion. These results suggest that at physiological concentrations of extracellular Ca2+ the mechanism by which alpha-adrenergic agonists mobilize cellular Ca2+ is different from that involving vasopressin and angiotensin. It seems that the hormones may have quite diverse effects on Ca2+ transport across the plasma membrane and perhaps organellar membranes in liver.

scholarly journals Binding and uptake of [3H]adrenaline by perfused rat liver

1984 ◽  
Vol 218 (3) ◽  
pp. 765-773 ◽  
Author(s):  
P H Reinhart ◽  
W M Taylor ◽  
F L Bygrave
Keyword(s):  
Rat Liver ◽  
Significant Proportion ◽  
Induced Responses ◽  
Perfused Rat Liver ◽  
Adrenergic Agonist ◽  
Related Factors ◽  
Pharmacological Agents ◽  
Total Inhibition ◽  
Alpha Adrenergic Agonist

The binding and uptake of [3H]adrenaline by the intact perfused rat liver was investigated. We showed that the administration of [3H]adrenaline to liver resulted in the rapid uptake of the radioligand, and that such uptake was independent of any Ca2+ redistributions induced by the hormone. At low adrenaline concentrations (less than 50 nM) uptake was inhibited by prazosin, whereas at higher hormone concentrations a significant proportion of total [3H]adrenaline uptake could not be inhibited by this antagonist. [3H]Adrenaline uptake could be directly correlated with adrenaline-induced responses such as an increased rate of respiration and glycogenolysis. The partial inhibition (approx. 25%) of [3H]adrenaline uptake by antagonists was sufficient for the total inhibition of hormone-induced responses. The effect of various pharmacological agents on [3H]adrenaline uptake was investigated, and the contribution of tissue-related factors to alpha-adrenergic agonist-antagonist interactions in vivo is discussed.

scholarly journals Ganglioside incorporation and release by the isolated perfused rat liver

1991 ◽  
Vol 274 (2) ◽  
pp. 581-585 ◽  
Author(s):  
S C Kivatinitz ◽  
A Miglio ◽  
R Ghidoni
Keyword(s):  
Rat Liver ◽  
The Other ◽  
Regulatory Role ◽  
Isolated Perfused Rat Liver ◽  
Order Kinetic ◽  
Perfused Rat Liver ◽  
Ganglioside Gm1 ◽  
First Order ◽  
Pseudo First Order

The fate of exogenous ganglioside GM1 labelled in the sphingosine moiety, [Sph-3H]GM1, administered as a pulse, in the isolated perfused rat liver was investigated. When a non-recirculating protocol was employed, the amount of radioactivity in the liver and perfusates was found to be dependent on the presence of BSA in the perfusion liquid and on the time elapsed after the administration of the ganglioside. When BSA was added to the perfusion liquid, less radioactivity was found in the liver and more in the perfusate at each time tested, for up to 1 h. The recovery of radioactivity in the perfusates followed a complex course which can be described by three pseudo-first-order kinetic constants. The constants, in order of decreasing velocity, are interpreted as: (a) the dilution of the labelled GM1 by the constant influx of perfusion liquid; (b) the washing off of GM1 loosely bound to the surface of liver cells; (c) the release of gangliosides from the liver. Process (b) was found to be faster in the presence of BSA, probably owing to the ability of BSA to bind gangliosides. The [Sph-3H]GM1 in the liver underwent metabolism, leading to the appearance of products of anabolic (GD1a, GD1b) and catabolic (GM2, GM3) origin; GD1a appeared before GM2 and GM3 but, at times longer than 10 min, GM2 and GM3 showed more radioactivity than GD1a. At a given time the distribution of the radioactivity in the perfusates was quite different from that of the liver. In fact, after 60 min GD1a was the only metabolite present in any amount, the other being GM3, the quantity of which was small. This indicates that the liver is able to release newly synthesized gangliosides quite specifically. When a recirculating protocol was used, there were more catabolites and less GD1a than with the non-recirculating protocol. A possible regulatory role of ganglioside re-internalization on their own metabolism in the liver is postulated.

Role of pyruvate transporter in the regulation of pyruvate dehydrogenase multienzyme complex in perfused rat liver

Biochemistry ◽  
1982 ◽  
Vol 21 (2) ◽  
pp. 346-353 ◽  
Author(s):  
Franz Maximilian Zwiebel ◽  
Ursula Schwabe ◽  
Merle S. Olson ◽  
Roland Scholz
Keyword(s):  
Rat Liver ◽  
Pyruvate Dehydrogenase ◽  
Multienzyme Complex ◽  
Perfused Rat Liver
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