Abstract
Intrinsic laryngeal muscles (ILM) are highly specialized muscles involved in phonation and airway protection, with unique properties that allow them to perform extremely rapid contractions and to escape from damage in muscle dystrophy. Due to that, they may differ from limb muscles in several physiological aspects. Because a better ability to handle intracellular calcium has been suggested to explain ILM unique properties, we hypothesized that the profile of the proteins that regulate calcium levels in ILM is different from that in a limb muscle. Calcium-related proteins were analyzed in the ILM, cricothyroid (CT), and tibialis anterior (TA) muscles from male Sprague–Dawley rats (8 weeks of age) using quantitative PCR and western blotting. Higher expression of key Ca2+ regulatory proteins was detected in ILM compared to TA, such as the sarcoplasmic reticulum (SR) Ca2+-reuptake proteins (Sercas 1 and 2), the Na+/Ca2+ exchanger, phospholamban, and the Ca2+-binding protein calsequestrin. Parvalbumin, calmodulin and the ATPase, Ca2+-transporting, and plasma membrane 1 were also expressed at higher levels in ILM compared to TA. The store-operated calcium entry channel molecule was decreased in ILM compared to the limb muscle and the voltage-dependent L-type and ryanodine receptor were expressed at similar levels in ILM and TA. These results show that ILM have a calcium regulation system profile suggestive of a better ability to handle calcium changes in comparison to limb muscles, and this may provide a mechanistic insight for their unique pathophysiological properties.
Highlights
The intrinsic laryngeal muscles (ILM) are highly specialized muscles involved in vital functions that include respiration, phonation, and airway protection (Hinrichsen and Dulhunty 1982; DelGaudio et al 1995; Hoh 2005)
In the mdx mouse model of Duchenne muscle dystrophy (DMD) (Bulfield et al 1984), we have suggested that ILM differ from the affected limb muscles in terms of their ability to handle changes in calcium due to differential levels of calcium-buffering proteins (Ferretti et al 2009), to what is observed in the extraocular muscles, which are protected in dystrophy (Khurana et al 1995; Porter et al 1998)
We found that the Ca2+ reuptake-related proteins of the sarcoplasmic reticulum, Serca1 and Serca2, the Serca regulator Pln and the Ca2+-binding protein Casq1 and Casq2 were expressed at higher mRNA levels in rat ILM compared to limb muscle
Summary
The intrinsic laryngeal muscles (ILM) are highly specialized muscles involved in vital functions that include respiration, phonation, and airway protection (Hinrichsen and Dulhunty 1982; DelGaudio et al 1995; Hoh 2005). These functions are possible due to ILM unique features that include specific fiber-type composition, high speed contraction, and resistance to fatigue (Hinrichsen and Dulhunty 1982; Hoh 2005). While ILM are involved early in myasthenia gravis, amyotrophic lateral sclerosis with bulbar involvement, and mitochondrial myopathy (Debain et al 1968; Mao et al 2001), they are histologically spared in Duchenne muscle dystrophy (DMD), except for the CT muscle (Marques et al 2007; Thomas et al 2008; Smythe 2009)
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