Key result
Inorganic phosphate and its diprotonated form were correlated with isometric force at the end of stimulation but not at maximal force, indicating they are not direct effectors of fatigue.
Inorganic phosphate and its diprotonated form are not direct effectors of fatigue in rat gastrocnemius muscle, suggesting a time-dependent and indirect effect possibly mediated by calcium ions.
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Phosphate unlikely direct fatigue effector in rat muscle; leaves open calcium-mediated mechanisms for mechanistic studies.
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.
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Giannesini et al. (2001) studied this question. Inorganic phosphate (P(i)) and H(2)PO(4)(-) was evaluated on Isometric force (F). Inorganic phosphate and its diprotonated form were correlated with isometric force at the end of stimulation but not at maximal force, indicating they are not direct effectors of fatigue.
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