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Progressive Disorganization of the Excitation–Contraction Coupling Apparatus in Aging Human Skeletal Muscle as Revealed by Electron Microscopy: A Possible Role in the Decline of Muscle Performance

¹ Interuniversity Institute of Myology, Ce.S.I. Center of Research on Aging, University G. d'Annunzio, Chieti, Italy.
² San Liberatore Hospital, Atri, Italy.

Address correspondence to Feliciano Protasi, PhD, Associate Professor, CeSI, Centro Scienze dell'Invecchiamento, Università degli Studi G. d'Annunzio, Chieti, CH I-66013, Italy. E-mail: fprotasi{at}unich.it

An impairment of the mechanisms controlling the release of calcium from internal stores (excitation–contraction [EC] coupling) has been proposed to contribute to the age-related decline of muscle performance that accompanies aging (EC uncoupling theory). EC coupling in muscle fibers occurs at the junctions between sarcoplasmic reticulum and transverse tubules, in structures called calcium release units (CRUs). We studied the frequency, cellular localization, and ultrastructure of CRUs in human muscle biopsies from male and female participants with ages ranging from 28 to 83 years. Our results show significant alterations in the CRUs' morphology and cellular disposition, and a significant decrease in their frequency between control and aged samples: 24.4/100 µm² (n = 2) versus 11.6/100 µm² (n = 7). These data indicate that in aging humans the EC coupling apparatus undergoes a partial disarrangement and a spatial reorganization that could interfere with an efficient delivery of Ca²⁺ ions to the contractile proteins.

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