Time-dependent and indirect effect of inorganic phosphate on force production in rat gastrocnemius exercising muscle determined by 31P-MRS.
The relationship of inorganic phosphate (P(i)) and its diprotonated form (H(2)PO(4)(-)) to isometric force (F) was analyzed non-invasively using 31P-magnetic resonance spectroscopy. Rat gastrocnemius muscles were electrically stimulated at six different frequencies in order to produce different levels of fatigue. A curvilinear relationship was demonstrated between force production and [P(i)] and [H(2)PO(4)(-)] accumulation. [P(i)] and [H(2)PO(4)(-)] were correlated with F at the end of the stimulation period but not when F was maximal at the early stage of the stimulation period. Interestingly, the respective [P(i)] and [H(2)PO(4)(-)] did not differ significantly between these two stages demonstrating that [P(i)] and [H(2)PO(4)(-)] cannot be considered as direct effectors of fatigue. This time-dependent and indirect effect of [P(i)] and [H(2)PO(4)(-)] on force production might be mediated by calcium ions.
Giannesini
B
B
Centre de Résonance Magnétique Biologique et Médicale (CRMBM), UMR CNRS 6612, Faculté de Médecine de Marseille, 27 Boulevard Jean Moulin, 13005, Marseille, France.
Izquierdo
M
M
Confort-Gouny
S
S
Cozzone
P J
PJ
Bendahan
D
D
D000818:Animals; D004558:Electric Stimulation; D007537:Isometric Contraction / Q000187:drug effects* / Q000502:physiology; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism / Q000494:pharmacology*; D010756:Phosphoric Acids / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D010710:Phosphates; D010756:Phosphoric Acids; C030242:phosphoric acid