Cigarette smoke directly impairs skeletal muscle function through capillary regression and altered myofibre calcium kinetics in mice

Abstract

Cigarette smokers exhibit exercise intolerance before a decline in respiratory function. In the present study, the direct effects of cigarette smoke on limb muscle function were tested by comparing cigarette smoke delivered to mice by weekly injections of cigarette smoke extract (CSE), or nose-only exposure (CS) 5 days each week, for 8 weeks. Cigarette smoke delivered by either route did not alter pulmonary airspace size. Muscle fatigue measured in situ was 50% lower in the CSE and CS groups than in control. This was accompanied by 34% and 22% decreases in soleus capillary-to-fibre ratio of the CSE and CS groups, respectively, and a trend for fewer skeletal muscle actin-positive arterioles (P = 0.07). In addition, fewer quiescent satellite cells (Nes+Pax7+) were associated with soleus fibres in mice with skeletal myofibre VEGF gene deletion (decreased 47%) and CS exposed (decreased 73%) than with control fibres. Contractile properties of isolated extensor digitorum longus and soleus muscles were impaired. In flexor digitorum brevis myofibres isolated from CSE mice, fatigue resistance was diminished by 43% compared to control and CS myofibres, and this was accompanied by a pronounced slowing in relaxation, an increase in intracellular Ca accumulation, and a slowing in sarcoplasmic reticulum Ca uptake. These data suggest that cigarette smoke components may impair hindlimb muscle vascular structure, fatigue resistance and myofibre calcium handling, and these changes ultimately affect contractile efficiency of locomotor muscles independent of a change in lung function.

Incubation with sodium nitrite attenuates fatigue development in intact single mouse fibres at physiological

“…Moreover, since the rate of SR Ca 2+ pumping is inversely related to basal [Ca 2+ ] c accumulation during repetitive contractions (Nogueira et al . , ), the lower basal [Ca 2+ ] c accumulation during the fatigue‐inducing contraction protocol would also probably have contributed to the better maintenance of SR Ca 2+ pumping during the NO 2 − trial. Lowering the energy cost of actomyosin ATPase, through inhibiting cross‐bridge cycling, has also been reported to abate the progressive slowing in SR Ca 2+ pumping rate during fatiguing contractions (Nogueira et al .…”

“…After killing, the FDB muscles from both posterior feet were quickly excised and individual, intact single muscle fibres (total of 28 fibres used in this study) were microdissected from the whole muscle and transferred to an intact muscle fibre system (model 1500A with force transducer model 403A, Aurora Scientific Inc., Aurora, ON, Canada), as described previously (Nogueira et al . ). The intact muscle fibre system was placed on the stage of a Nikon inverted microscope with a 40× long distance Fluor objective.…”

“…Cytosolic calcium concentration ([Ca 2+ ] c ) and intracellular pH (pH i ) changes were obtained by fluorescence spectroscopy using a Photon Technology International illumination and detection system (DeltaScan model) (Nogueira et al . ).…”

“…During the contraction protocols, SR Ca 2+ pumping was measured using the procedures described by (Nogueira et al . ). Briefly, a SR Ca 2+ pumping curve was obtained by plotting the rate of [Ca 2+ ] c decline (−d[Ca 2+ ] c /d t ) during the elevated long tail of [Ca 2+ ] c decay (from 100 ms to 3 s after the stimulation period) versus [Ca 2+ ] c (eqn ).…”

“…These values were based on mean values of 4.4 ± 0.4 for N and 32 ± 9 and for L obtained in individual experiments ( n = 5 fibres), with a maximum increase in least‐square error of 15% (Nogueira et al . ).…”