Different effects of gradual vs. acute adenine nucleotide depletion on ATP cost of muscle contraction.
ATP and phosphocreatine (PCr) levels were chronically reduced in rat fast-twitch muscle by 40 and 87%, respectively, after rats were fed a diet containing 1% beta-guanidinopropionate (beta-GPA) for 9 wk. Myosin heavy chain distribution of superficial gastrocnemius muscle changed from 22:78% type IIA/type IIB in control to 39:61% in GPA-treated muscles. ATP cost of contractions was estimated from the PCr changes measured by gated 31P-nuclear magnetic resonance after brief (< 6 s) bursts of contractions. There was no significant change in the ATP cost of either twitch (0.3 mumol.g-1.twitch-1) or tetanic (2.5 mumol.g-1.100 ms tetanus-1) contractions in gastrocnemius muscle after chronic phosphagen depletion due to beta-GPA feeding. In two other groups of rats, ATP of gastrocnemius muscles was acutely depleted to inosine 5'-monophosphate (IMP) by tetanic stimulation. IMP reanimation was inhibited during a subsequent 75-min recovery period in one group by hadacidin treatment (100 mg/kg), resulting in 46% ATP depletion compared with the similarly stimulated and recovered control group. In contrast to gradual ATP depletion due to beta-GPA feeding, this acute ATP depletion treatment was associated with a 39% decrease in ATP cost of twitch contractions.
Department of Physical Education and Exercise Science, Michigan State University, East Lansing 48824.
J M
JM
Foley
G R
GR
Adams
R A
RA
Meyer
D000227:Adenine Nucleotides / Q000172:deficiency*; D000255:Adenosine Triphosphate / Q000172:deficiency / Q000378:metabolism*; D000818:Animals; D004032:Diet; D006146:Guanidines / Q000008:administration & dosage / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D011422:Propionates / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D000227:Adenine Nucleotides; D006146:Guanidines; D007527:Isoenzymes; D011422:Propionates; D000255:Adenosine Triphosphate; D009218:Myosins; C005775:guanidinopropionic acid