Phosphorus nuclear magnetic resonance studies on the effect of duration of contraction in bull‐frog skeletal muscles.

SUMMARY1. The effect of sarcomere length (SL) during a fatiguing series of isometric tetani of frog muscle fibres was investigated. Tetani at 2-3 ,um SL were more fatiguing than tetani at 3-2 ,sm SL, in that force declined twice as much and relaxation became much slower.2. In a second set of experiments the force and heat production were measured during a series of fatiguing tetani. Heat was separated into two components: (a) crossbridge heat which is dependent on filament overlap and interaction, and (b) non-crossbridge heat which is independent of filament overlap and due to Ca2" turnover.3. In a series of fifty tetani, force, crossbridge heat and non-crossbridge heat each declined by 25-30 % of its initial value.4. The 25 % reduction in non-crossbridge heat occurred completely during the first few tetani of the fatiguing series while force declined by less than 3 %. This may be due to a reduction in Ca2" binding to parvalbumin and to Ca2' remaining bound during the remainder of the fatigue series.5. After the first few tetani of the fatigue series the non-crossbridge heat hardly changed as force declined by a further 25 % of its initial value. Continuing reduction of force with constant Ca21 turnover indicates a reduction in the Ca21 sensitivity of the filaments, and/or a reduction in the average force per attached crossbridge.6. At the start of the fatiguing series, as force declines by about 7-5 % there is a much larger decline of crossbridge heat (17 %). The reason for this is unknown. Later in the series, force declined more rapidly than heat. This is probably due to a progressive accumulation of inorganic phosphate which acts by depressing force more than it depresses ATP breakdown.

Section: Interpretation Of Changes In Non-crossbridge Heatmentioning

confidence: 98%

Changes in crossbridge and non‐crossbridge energetics during moderate fatigue of frog muscle fibres.

Barclay

Curtin

Woledge

1993

“…It is very likely that Pi concentration increases in moderate fatigue studied here; Kawano, Tanokura & Yamada (1988) have measured the time constant for recovery of P1 to its initial value to be approximately 30 min after a tetanus of frog muscle at 4 'C. The time constant was independent of tetanus duration in the range tested, 0 2-10 s. Pi recovery would therefore not be complete under the moderate fatigue conditions used here, so Pi concentration would increase.…”

Section: Acidification Pi and Fatiguementioning

confidence: 99%

Force‐velocity relation for frog muscle fibres: effects of moderate fatigue and of intracellular acidification.

Curtin

Edman

1994

1. Intact frog single fibres were investigated under control conditions (1 s tetanus every 2, 3 or 5 min) and during moderate fatigue (interval between tetani 15 or 30 s).2. Fatigue reduced isometric force (PO) by 25-8 + 1-6 % (S.E.M.; n = 13) and depressed the maximum velocity of shortening (Vm&x) by 10-2 ± 2+2 % (n = 13). The force-velocity relation became less curved, a/PO* (see Methods) being increased by 29-5 + 8-8 % (n = 13).Thus, power was less affected than isometric force or Vmax.3. The velocity of unloaded shortening (VO), from slack test measurements, was reduced proportionally more than Vmax during fatigue. Under control conditions VO was larger than Vmax, but during fatigue their values were not significantly different. 4. Stiffness during shortening was reduced during fatigue indicating fewer attached crossbridges in fatigue. Force was reduced more than stiffness indicating that, on average, there is less force per attached cross-bridge. 5. The force-lengthening velocity relation showed that the ability to resist forces greater than isometric was well preserved in fatigue. 6. Compared with fatigue, intracellular acidification with CO2 produced a smaller reduction in isometric force. However, reduction in Vm&x was not significantly different from that in fatigue. These results are consistent with both inorganic phosphate and H+ increasing in fatigue, but only H+ increasing during acidification, and isometric force being reduced by both, Vmax being sensitive only to H+.

“…The methods are similar to those described previously (in more detail) by Kawano et al (1988). A muscle chamber (muscle holder and 20 mm NMR sample tube) was used in which eight pairs of soleus muscles were mounted.…”

Section: Nmr Measurementsmentioning

confidence: 99%

“…Studies in toad and frog muscle have already revealed post-contractile PCr splitting at certain temperatures (Yamada & Tanokura, 1983; Kawano, Tanokura & Yamada, 1988).…”

Section: Introductionmentioning

confidence: 99%

The time course of phosphate metabolites and intracellular pH using 31P NMR compared to recovery heat in rat soleus muscle.

Phillips

Takei

Yamada

1993

Self Cite

SUMMARY1. The recovery time course of changes in phosphate metabolites and pH, after tetanic contractions of 6 and 9 s were studied using 31P NMR with 4 and 16 s resolution, in rat soleus muscles at 20 'C. Muscles were at a sarcomere length of 3 15 ,um (active), being greater than optimum for force which was 2-88 ,um (active).2. The post-contraction recovery of chemical changes was compared with the heat production in parallel experiments. Initial and recovery heat production were measured in tetanically stimulated muscles.3. During recovery from tetanic contractions the changes in phosphocreatine (PCr) matched the changes in inorganic phosphate (Pi). The change in intracellular pH (pHi) was biphasic. The pHi first became more alkaline after contraction and then decreased until it reached a point below the baseline value. There was then a final recovery. 4. The initial heat and recovery heat production were greater than that expected from the PCr hydrolysis estimated during the tetanus and the PCr resynthesis that follows.5. These data support the presence of 'unexplained heat' during a contraction and its related recovery processes in rat soleus muscle.