HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Cieslar, J. H. Articles by Dobson, G. P. Search for Related Content PubMed PubMed Citation Articles by Cieslar, J. H. Articles by Dobson, G. P. Social Bookmarking                      What's this?

J Biol Chem, Vol. 275, Issue 9, 6129-6134, March 3, 2000

Free [ADP] and Aerobic Muscle Work Follow at Least Second Order Kinetics in Rat Gastrocnemius in Vivo^*

Julie H. Cieslar and Geoffrey P. Dobson

From the Department of Physiology and Pharmacology, Schools of Biomolecular and Molecular Sciences, James Cook University, Townsville, Queensland 4811, Australia

The relationship between free cytosolic [ADP] (and [P_i]) and steady-state aerobic muscle work in rat gastrocnemius muscle in vivo using ³¹P NMR was investigated. Anesthetized rats were ventilated and placed in a custom-built cradle fitted with a force transducer that could be placed into a 7-tesla NMR magnet. Muscle work was induced by supramaximal sciatic nerve stimulation that activated all fibers. Muscles were stimulated at 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 1.0, and 2.0 Hz until twitch force, phosphocreatine, and P_i were unchanged between two consecutive spectra acquired in 4-min blocks (8-12 min). Parallel bench experiments were performed to measure total tissue glycogen, lactate, total creatine, and pyruvate in freeze-clamped muscles after 10 min of stimulation at each frequency. Up to 0.5 Hz, there was no significant change in muscle glycogen, lactate, and the lactate/pyruvate ratios between 8-12 min. At 0.8 Hz, there was a 17% fall in glycogen and a 65% rise in the muscle lactate with a concomitant fall in pH. Above this frequency, glycogen fell rapidly, lactate continued to rise, and ATP and pH declined. On the basis of these force and metabolic measurements, we estimated the maximal mitochondrial capacity (V_max) to be 0.8 Hz. Free [ADP] was then calculated at each submaximal workload from measuring all the reactants of the creatine kinase equilibrium after adjusting the K'_CK to the muscle temp (30 °C), pH, and pMg. We show that ADP (and P_i) and tension-time integral follow a Hill relationship with at least a second order function. The K_0.5 values for free [ADP] and [P_i] were 48 µM and 9 mM, respectively. Our data did not fit any form of the Michaelis-Menten equation. We therefore conclude that free cytosolic [ADP] and [P_i] could potentially control steady-state oxidative phosphorylation in skeletal muscle in vivo.

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				G. P. Dobson, S. Hitchins, and W. E. Teague Jr. Thermodynamics of the Pyruvate Kinase Reaction and the Reversal of Glycolysis in Heart and Skeletal Muscle J. Biol. Chem., July 19, 2002; 277(30): 27176 - 27182. [Abstract] [Full Text] [PDF]

				F. Joubert, J.-L. Mazet, P. Mateo, and J. A. Hoerter 31P NMR Detection of Subcellular Creatine Kinase Fluxes in the Perfused Rat Heart. CONTRACTILITY MODIFIES ENERGY TRANSFER PATHWAYS J. Biol. Chem., May 17, 2002; 277(21): 18469 - 18476. [Abstract] [Full Text] [PDF]

				J. H. Cieslar and G. P. Dobson Force reduction uncoupled from pH and H2PO4- in rat gastrocnemius in vivo with continuous 2-Hz stimulation Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2001; 281(2): R511 - R518. [Abstract] [Full Text] [PDF]