Contractile properties of in situ perfused skeletal muscles from rats with congestive heart failure

Abstract

We hypothesized that in congestive heart failure (CHF) slow‐twitch but not fast‐twitch muscles exhibit decreased fatigue resistance in the sense of accelerated reduction of muscle force during activity. Experiments were carried out on anaesthetized rats 6 weeks after induction of myocardial infarction or a sham operation (Sham). Animals with left ventricular end‐diastolic pressure (LVEDP) > 15 mmHg under anaesthesia were selected for the CHF group. There was no muscle atrophy in CHF. Force generation by in situ perfused soleus (Sol) or extensor digitorum longus (EDL) muscles was recorded during stimulation (trains at 5 Hz for 6 s (Sol) or 10 Hz for 1.5 s (EDL) at 10 or 2.5 s intervals, respectively) for 1 h in Sol and 10 min in EDL at 37 °C. Initial force was almost the same in Sol from CHF and Sham rats, but relaxation was slower in CHF. Relaxation times (95–5 % of peak force) were 177 ± 55 and 131 ± 44 ms in CHF and Sham, respectively, following the first stimulation train. After 2 min of stimulation the muscles transiently became slower and maximum relaxation times were 264 ± 71 and 220 ± 45 ms in CHF and Sham, respectively (P < 0.05). After 60 min they recovered to 204 ± 60 and 122 ± 55 ms in CHF and Sham, respectively (P < 0.05). In CHF but not in Sham rats the force of contraction of Sol declined from the second to the sixtieth minute to 70 % of peak force. The EDL of both CHF and Sham fatigued to 24–28 % of initial force, but no differences in contractility pattern were detected. Thus, slow‐twitch muscle is severely affected in CHF by slower than normal relaxation and significantly reduced fatigue resistance, which may explain the sensation of both muscle stiffness and fatigue in CHF patients.

Enhanced matrix metalloproteinase activity in skeletal muscles of rats with congestive heart failure

“…Interestingly, in our hands, muscles from CHF rats develop the same maximal force as muscles from Sham rats in the absence of activity before the contractions (17). Thus increased MMP activity apparently does not prevent normal function in a muscle at the onset of exercise.…”

“…Several long-term studies report a transition toward a faster skeletal muscle phenotype, but this seems not to be the case in short-term studies (16). However, in our rat model of CHF, atrophy and fiber type conversion do not take place (17). On the other hand, we have noted that the fast-twitch flexor digitorum brevis muscle was more fragile during dissection of single fibers in the CHF than in the Sham rat (15), and Perreault et al (21) found alterations in contractility and Ca 2ϩ handling in the fast-twitch EDL muscle in rats 6 wk after induction of heart failure.…”

Effects of Congestive Heart Failure on Ca 2+ Handling in Skeletal Muscle During Fatigue

“…7,9,25 Surprisingly the force decrease in CHF soleus fibers was not accompanied by any decrease in tetanic [Ca 2ϩ ] i . This is in contrast to the findings in the Sham soleus fibers as well as our previously reported observations in fast-twitch fibers of both CHF and Sham rats, where there was a clear relationship between the decrease in tetanic force and [Ca 2ϩ ] i .…”

“…Further characteristics of the present rat model of CHF have been reported by us previously. 9,11,21 The weight and water content of soleus and EDL muscles were not significantly different between CHF and Sham groups at any time point (supplemental Table I). Thus, CHF caused no apparent muscle atrophy or edema.…”

Global cooling: Cold acclimation and the expression of soluble proteins in carp skeletal muscle

“…Although muscle plasticity is well established, comparative approaches to investigate phenotypic responses in muscle typically rely upon nonphysiological adaptations such as denervation [1] or pathological processes [2] to produce a measurable effect at the molecular level. Such dramatic changes in phenotype can often prove incapacitating or fatal in vertebrates.…”