Cieslar, Julie H., and Dobson, Geoffrey P. (2001) Force reduction uncoupled from pH an H2PO4 in rat gastrocnemius in vivo with continuous 2-Hz stimulation. American Journal of Physiology-Regulatory Integrative and Comparative Physiology, 281 (2). R511-R518.

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Abstract

The aim of this study was to examine the effect of the products of ATP hydrolysis on the fatigue process in rat gastrocnemius in vivo. Adult male Sprague-Dawley rats (300–400 g) were anesthetized and ventilated in a custom-built cradle fitted with a force transducer that could be placed into a 7-T NMR magnet. The muscle was stimulated continuously at 2 Hz for 20 min (n = 7). Isometric twitch force increased in the first 4 min of stimulation accompanied by changes in twitch duration (20% increase in relaxation time). Prolonged relaxation was associated with changes in cytosolic pH (6.91 to 6.58), lactate (1.8 to 12.6 μmol/g wet wt), and H2PO Formula (7.57 to 13.99 mM). After 4 min, relaxation time, pH, lactate, and H2PO Formula returned toward control values as twitch force progressively decreased. No correlation was found between force decline (or twitch broadening) and total phosphate (3 to 23 mM), free [ADP] (18 to 95 μM), free [Mg2+] (0.58 to 0.96 mM), or free energy of ATP hydrolysis (−65 to −55 kJ/mol). We conclude that force decline is not due to increased pH and/or H2PO Formula but to fatigue of the fast-twitch fibers, possibly linked to glycogen depletion and/or failure of nerve impulse transmission in these fibers.

Item ID:	13068
Item Type:	Article (Research - C1)
ISSN:	0363-6119
Keywords:	adenosine 5′-triphosphate, adenosine diphosphate, inorganic phosphate, muscle work, phosphorus-31 nuclear magnetic resonance
Funders:	Australian Research Council (ARC)
Date Deposited:	28 Feb 2013 01:42
FoR Codes:	11 MEDICAL AND HEALTH SCIENCES > 1116 Medical Physiology > 111602 Human Biophysics @ 51% 10 TECHNOLOGY > 1004 Medical Biotechnology > 100499 Medical Biotechnology not elsewhere classified @ 49%
SEO Codes:	92 HEALTH > 9299 Other Health > 929999 Health not elsewhere classified @ 100%
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