Contractile dysfunction and altered metabolic profile of the aging rat thyroarytenoid muscle

Abstract

The larynx and its muscles are important for ventilation, coughing, sneezing, swallowing, Valsalva's maneuver, and phonation. Because of their functional demands, the intrinsic laryngeal muscles have a unique phenotype: very small and fast fibers with high mitochondrial content. How aging affects their function is largely unknown. In this study, we tested the hypothesis that an intrinsic laryngeal muscle (thyroarytenoid muscle, a vocal fold adductor) would become weaker, slower, and fatigable with age. Muscles from Fischer 344 x Brown Norway F1 hybrid rats (6, 18, and 30 mo of age) were used for in vitro contractile function and histology. Thyroarytenoid muscles generated significantly lower twitch and tetanic forces at 30 mo vs. 6 and 18 mo. Maximal shortening velocity decreased by 20% at 30 mo (vs. 6 mo), and velocity of unloaded shortening was slower at 18 and 30 mo by 19 and 27% vs. 6 mo. There was no histochemical evidence of altered myosin ATPase activity at 18 or 30 mo of age. Fatigue resistance was significantly decreased at 18 and 30 mo. We also found abundant mitochondrial clusters and ragged red fibers in the muscles of 30-mo-old rats, and there was an age-related increase in glycogen-positive fibers. We conclude that rat thyroarytenoid muscles become weaker, slower, and more fatigable with age. These functional changes are not due to alterations in myosin ATPase activity, but a switch in the expression of myosin isoforms remains a possibility. Finally, the alterations in mitochondrial and glycogen content indicate a shift in the metabolic characteristics of these muscles with age.

Aging Thyroarytenoid and Limb Skeletal Muscle: Lessons in Contrast

“…In animal models, these modifications are of sufficient magnitude to alter the muscle's contractile properties toward a slower, weaker, and less fatigue-resistant profile. 71 Likely contributors to the structural and functional changes include myelinization alterations within the RLN and SLN, reduced number of axonal terminals, decreased vascular support, systemic hormonal changes, and stochastic damage. [110][111][112][113][114]133,142,[146][147][148]183,184 The above discussion has also highlighted the distinctive nature of the TA muscle.…”

“…The question remains as to whether the sarcopenic features of limb skeletal muscle can be generalized to other muscles throughout the body. Some have argued that muscles of the head and neck are unique in their morphology as well as in their response to aging 70,71 and that these muscles should, therefore, be considered separately during studies of age-related decline. Below is a review of the morphological changes observed with age and the primary influences or domains associated with these changes.…”

“…Abnormal accumulations of mitochondria 10,71 Vascular Altered vasodilation 129,130 Reduced blood flow Reduced capillary surface area 111…”

“…At least two studies have identified abnormal accumulations of mitochondria within aged TA muscle fibers, a finding suggestive of age-related mitochondrial deficits. 10,71 Interestingly, McMullen and Andrade 71 found that aged rats demonstrating the increased mitochondrial content also displayed a reduction in fatigue resistance and an increase in glycogen content. The authors proposed that the age-related mitochondrial dysfunction within the TA may actually alter contractile properties of the muscle by prompting a shift toward a more glycolytic profile.…”

Effect of Aging on Tongue Protrusion Forces in Rats

“…In prior studies, tongue twitch contraction times for evoked retrusive tongue actions was prolonged in old rats when compared with young, while there was no difference in twitch half-decay times [15]. Conversely, in rat larynx (thyroarytenoid muscle), halfdecay time was prolonged in old animals without a concurrent extension of twitch contraction time [16]. Accordingly, our goal was to examine these temporal elements for evoked protrusive tongue actions in old vs. young rat tongue.…”