{"doi":"10.1152/ajpcell.00291.2005","title":"μ-Calpain and calpain-3 are not autolyzed with exhaustive exercise in humans","abstract":"<jats:p> μ-calpain and calpain-3 are Ca<jats:sup>2+</jats:sup>-dependent proteases found in skeletal muscle. Autolysis of calpains is observed using Western blot analysis as the cleaving of the full-length proteins to shorter products. Biochemical assays suggest that μ-calpain becomes proteolytically active in the presence of 2–200 μM Ca<jats:sup>2+</jats:sup>. Although calpain-3 is poorly understood, autolysis is thought to result in its activation, which is widely thought to occur at lower intracellular Ca<jats:sup>2+</jats:sup> concentration levels ([Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>; ∼1 μM) than the levels at which μ-calpain activation occurs. We have demonstrated the Ca<jats:sup>2+</jats:sup>-dependent autolysis of the calpains in human muscle samples and rat extensor digitorum longus (EDL) muscles homogenized in solutions mimicking the intracellular environment at various [Ca<jats:sup>2+</jats:sup>] levels (0, 2.5, 10, and 25 μM). Autolysis of calpain-3 was found to occur across a [Ca<jats:sup>2+</jats:sup>] range similar to that for μ-calpain, and both calpains displayed a seemingly higher Ca<jats:sup>2+</jats:sup> sensitivity in human than in rat muscle homogenates, with ∼15% autolysis observed after 1-min exposure to 2.5 μM Ca<jats:sup>2+</jats:sup> in human muscle and almost none after 1- to 2-min exposure to the same [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub> level in rat muscle. During muscle activity, [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub> may transiently peak in the range found to autolyze μ-calpain and calpain-3, so we examined the effect of two types of exhaustive cycling exercise (30-s “all-out” cycling, n = 8; and 70% V̇o<jats:sub>2 peak</jats:sub> until fatigue, n = 3) on the amount of autolyzed μ-calpain or calpain-3 in human muscle. No significant autolysis of μ-calpain or calpain-3 occurred as a result of the exercise. These findings have shown that the time- and concentration-dependent changes in [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub> that occurred during concentric exercise fall near but below the level necessary to cause autolysis of calpains in vivo. </jats:p>","journal":"American Journal of Physiology-Cell Physiology","year":2006,"id":675909,"datarank":2.1826792823725722,"base_score":4.02535169073515,"endowment":4.02535169073515,"self_citation_contribution":0.6038027536102726,"citation_network_contribution":1.5788765287622997,"self_endowment_contribution":0.6038027536102726,"citer_contribution":1.5788765287622997,"corpus_percentile":null,"corpus_rank":null,"citation_count":55,"citer_count":39,"citers_with_citation_signal":35,"citers_with_endowment":35,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":null,"is_data_producer":false,"deposit_databanks":null,"is_oa":false,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":null,"fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":1766058,"name":"Rodney J. 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Although calpain-3 is poorly understood, autolysis is thought to result in its activation, which is widely thought to occur at lower intracellular Ca<jats:sup>2+</jats:sup> concentration levels ([Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>; ∼1 μM) than the levels at which μ-calpain activation occurs. We have demonstrated the Ca<jats:sup>2+</jats:sup>-dependent autolysis of the calpains in human muscle samples and rat extensor digitorum longus (EDL) muscles homogenized in solutions mimicking the intracellular environment at various [Ca<jats:sup>2+</jats:sup>] levels (0, 2.5, 10, and 25 μM). Autolysis of calpain-3 was found to occur across a [Ca<jats:sup>2+</jats:sup>] range similar to that for μ-calpain, and both calpains displayed a seemingly higher Ca<jats:sup>2+</jats:sup> sensitivity in human than in rat muscle homogenates, with ∼15% autolysis observed after 1-min exposure to 2.5 μM Ca<jats:sup>2+</jats:sup> in human muscle and almost none after 1- to 2-min exposure to the same [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub> level in rat muscle. During muscle activity, [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub> may transiently peak in the range found to autolyze μ-calpain and calpain-3, so we examined the effect of two types of exhaustive cycling exercise (30-s “all-out” cycling, n = 8; and 70% V̇o<jats:sub>2 peak</jats:sub> until fatigue, n = 3) on the amount of autolyzed μ-calpain or calpain-3 in human muscle. No significant autolysis of μ-calpain or calpain-3 occurred as a result of the exercise. These findings have shown that the time- and concentration-dependent changes in [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub> that occurred during concentric exercise fall near but below the level necessary to cause autolysis of calpains in vivo. </jats:p>","is_dataset_classified":null,"base_score":4.02535169073515,"endowment":4.02535169073515,"datacite_reuse_total":0,"file_count":0,"downloads":0,"views":0,"has_version_chain":false,"is_dataset":false,"is_oa":false,"pmid":"16107503","pmcid":null,"openalex_id":"https://openalex.org/W2046968011","authors":[],"funders":[],"total_grants":0,"fwci":1.6231,"citation_percentile":0.81127214,"influential_citations":0,"citation_trend":[{"year":2012,"count":3},{"year":2013,"count":1},{"year":2014,"count":6},{"year":2015,"count":1},{"year":2016,"count":1},{"year":2017,"count":2},{"year":2018,"count":3},{"year":2019,"count":2},{"year":2020,"count":4},{"year":2021,"count":1},{"year":2022,"count":2},{"year":2023,"count":3},{"year":2024,"count":1},{"year":2025,"count":2}],"oa_status":"closed","license":null,"oa_locations":[{"url":"https://journals.physiology.org/doi/pdf/10.1152/ajpcell.00291.2005","host_type":"publisher"},{"url":"https://doi.org/10.1152/ajpcell.00291.2005","host_type":"journal"},{"url":"https://pubmed.ncbi.nlm.nih.gov/16107503","host_type":"repository"}],"fields_of_study":["Calpain Protease Function and Regulation","Venomous Animal Envenomation and Studies","Meat and Animal Product Quality","Animals","Autolysis","Calcium","Calpain","Humans","Isoenzymes","Male","Muscle Proteins","Muscle, Skeletal","Physical Endurance","Physical Exertion","Rats","Rats, Long-Evans","Time Factors"],"mesh_terms":["Animals","Autolysis","Calcium","Calpain","Physical Exertion","Humans","Isoenzymes","Male","Muscle Proteins","Physical Endurance","Time Factors","Muscle, Skeletal","Rats, Long-Evans","Rats"],"keywords":["Calpain","Autolysis (biology)","Calpastatin","Proteases","Intracellular","Skeletal muscle","Western blot","Chemistry","Biochemistry","Endocrinology","Internal medicine","Biology","Enzyme","Medicine"],"sdg_mappings":[],"linked_datasets":[],"clinical_trials":[],"software_tools":[],"database_accessions":[],"source":"live","citation_network_status":"fetched"},"created_at":"2026-08-17T01:52:01.970477Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}