Biomaterial Database

Role of cyclic AMP and inorganic phosphate in the regulation of muscle glycogenolysis during exercise. 1988

D Chasiotis

Hellenic Sports Research Institute, Olympic Sports Center of Athens, Greece.

The roles of cAMP and inorganic phosphate (Pi) in the regulation of muscle glycogenolysis during exercise have been investigated in humans using the needle biopsy technique. The fraction of phosphorylase a in resting muscle was as a mean 23%, but the rate of glycogenolysis was extremely low. Epinephrine infusion increased cAMP in muscle by 3-fold and transformed 80% of phosphorylase to the a form. Despite this, the rate of glycogenolysis was only 5-10% of the maximum rate of phosphorylase a (Vmax a) determined in vitro. Isometric exercise for 25 s at 66% MVC or electrical stimulation for 50 s at 20 Hz transformed about 53% and 80% of phosphorylase in the a form. The rate of glycogenolysis ranged between 50-90 mmol.kg-1.dm.min-1 and was close to Vmax of phosphorylase a determined in vitro. No significant difference in the rate of glycogenolysis in muscle was observed after isometric exercise to fatigue without and with epinephrine infusion, respectively. Apparently the rate of glycogenolysis in muscle is not solely related to the fraction of phosphorylase in the a form. Several factors could be responsible for allosteric and/or substrate regulation. The results in the present studies can be explained on the basis of substrate regulation of phosphorylase activity, provided that Pi is present in a limiting amount at the active site of phosphorylase in muscle at rest. It is concluded that transformation of phosphorylase b to a is important but alone is not adequate for a high activity and thus for a high rate of glycogenolysis in muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D009132	Muscles	Contractile tissue that produces movement in animals.	Muscle Tissue,Muscle,Muscle Tissues,Tissue, Muscle,Tissues, Muscle
D010710	Phosphates	Inorganic salts of phosphoric acid.	Inorganic Phosphate,Phosphates, Inorganic,Inorganic Phosphates,Orthophosphate,Phosphate,Phosphate, Inorganic
D010762	Phosphorylase a	The active form of GLYCOGEN PHOSPHORYLASE that is derived from the phosphorylation of PHOSPHORYLASE B. Phosphorylase a is deactivated via hydrolysis of phosphoserine by PHOSPHORYLASE PHOSPHATASE to form PHOSPHORYLASE B.
D004837	Epinephrine	The active sympathomimetic hormone from the ADRENAL MEDULLA. It stimulates both the alpha- and beta- adrenergic systems, causes systemic VASOCONSTRICTION and gastrointestinal relaxation, stimulates the HEART, and dilates BRONCHI and cerebral vessels. It is used in ASTHMA and CARDIAC FAILURE and to delay absorption of local ANESTHETICS.	Adrenaline,4-(1-Hydroxy-2-(methylamino)ethyl)-1,2-benzenediol,Adrenaline Acid Tartrate,Adrenaline Bitartrate,Adrenaline Hydrochloride,Epifrin,Epinephrine Acetate,Epinephrine Bitartrate,Epinephrine Hydrochloride,Epinephrine Hydrogen Tartrate,Epitrate,Lyophrin,Medihaler-Epi,Acetate, Epinephrine
D006003	Glycogen
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000242	Cyclic AMP	An adenine nucleotide containing one phosphate group which is esterified to both the 3'- and 5'-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and ACTH.	Adenosine Cyclic 3',5'-Monophosphate,Adenosine Cyclic 3,5 Monophosphate,Adenosine Cyclic Monophosphate,Adenosine Cyclic-3',5'-Monophosphate,Cyclic AMP, (R)-Isomer,Cyclic AMP, Disodium Salt,Cyclic AMP, Monoammonium Salt,Cyclic AMP, Monopotassium Salt,Cyclic AMP, Monosodium Salt,Cyclic AMP, Sodium Salt,3',5'-Monophosphate, Adenosine Cyclic,AMP, Cyclic,Adenosine Cyclic 3',5' Monophosphate,Cyclic 3',5'-Monophosphate, Adenosine,Cyclic Monophosphate, Adenosine,Cyclic-3',5'-Monophosphate, Adenosine,Monophosphate, Adenosine Cyclic
D015444	Exercise	Physical activity which is usually regular and done with the intention of improving or maintaining PHYSICAL FITNESS or HEALTH. Contrast with PHYSICAL EXERTION which is concerned largely with the physiologic and metabolic response to energy expenditure.	Aerobic Exercise,Exercise, Aerobic,Exercise, Isometric,Exercise, Physical,Isometric Exercise,Physical Activity,Acute Exercise,Exercise Training,Activities, Physical,Activity, Physical,Acute Exercises,Aerobic Exercises,Exercise Trainings,Exercise, Acute,Exercises,Exercises, Acute,Exercises, Aerobic,Exercises, Isometric,Exercises, Physical,Isometric Exercises,Physical Activities,Physical Exercise,Physical Exercises,Training, Exercise,Trainings, Exercise