Regulation of glucogen metabolism in liver by the autonomic nervous system VI. Possible mechanism of phosphorylase activation by the splanchnic nerve
T Shimazu, A Amakawa - Biochimica et Biophysica Acta (BBA)-General …, 1975 - Elsevier
T Shimazu, A Amakawa
Biochimica et Biophysica Acta (BBA)-General Subjects, 1975•ElsevierThe effects of autonomic-nerve stimulation on the activities of phosphorylase (EC 2.4. 1.1),
dephospho-phosphorylase kinase (EC 2.7. 1.38) and phosphorylase phosphatase (EC 3.1.
3.17), and on the concentration of adenosine 3′, 5′-monophosphate in rabbit liver were
investigated. Results were compared with the effects of epinephrine and glucagon on these
enzymes. 1. 1. The activity of liver phosphorylase increased rapidly and markedly on
electrical stimulation of the splanchnic nerve, or after intraportal administration of …
dephospho-phosphorylase kinase (EC 2.7. 1.38) and phosphorylase phosphatase (EC 3.1.
3.17), and on the concentration of adenosine 3′, 5′-monophosphate in rabbit liver were
investigated. Results were compared with the effects of epinephrine and glucagon on these
enzymes. 1. 1. The activity of liver phosphorylase increased rapidly and markedly on
electrical stimulation of the splanchnic nerve, or after intraportal administration of …
Abstract
The effects of autonomic-nerve stimulation on the activities of phosphorylase (EC 2.4.1.1), dephospho-phosphorylase kinase (EC 2.7.1.38) and phosphorylase phosphatase (EC 3.1.3.17), and on the concentration of adenosine 3′,5′-monophosphate in rabbit liver were investigated. Results were compared with the effects of epinephrine and glucagon on these enzymes.
- 1.1. The activity of liver phosphorylase increased rapidly and markedly on electrical stimulation of the splanchnic nerve, or after intraportal administration of epinephrine or glucagon. the activity was not affected by vagal stimulation.
- 2.2. The activity of dephospho-phosphorylase kinase increased about 2–3-fold 1 min after injections of epinephrine and glucagon, glucagon causing more activation than epinephrine. The enzyme activity was not altered by splanchnic-nerve, or vagal stimulation.
- 3.3. Injections of epinephrine and glucagon caused marked elevation of liver adenosine 3′,5′-monophosphate within a few minutes. With epinephrine, the nucleotide concentration rose to a maximum after 1 min and amounted to about 3-fold increase, while with glucagon the maximum increase of approximately 8-fold increase was observed after 2 min. Stimulation of the splanchnic nerve for 10 min did not affect the adenosine 3′,5′-monophosphate level in the liver. Vagal stimulation also had no effect on the level.
- 4.4. The activity of phosphorylase phosphatase decreased promptly (within 30 s) and markedly on splanchnic-nerve stimulation, but did not change significantly on administration of epinephrine or glucagon. A small but insignificant increase in phosphatase activity was observed upon vagal stimulation.
- 5.5. The effect of Ca2+ on purified dephospho-phosphorylase kinase was studied. The activity was found to depend partially on free Ca2+ at low Ca2+ concentrations (1 · 10−7−1 · 10−5 M).
- 6.6. These results suggest that the rise in hepatic phosphorylase content upon splanchnic-nerve stimulation, unlike that induced by epinephrine and glucagon, is not mediated by adenosine 3′,5′-monophosphate and subsequent activation of dephospho-phosphorylase kinase, but rather by inactivation of phosphorylase phosphatase. The possible existence of a new factor in this mechanism is discussed.
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