title: Mechanism of specific force deficit in the senescent rat diaphragm.
abstract: Aging is associated with a decline in the maximal in vitro specific force in the rat costal diaphragm. The purpose of this study was to determine if this force deficit is associated with a decrease in the concentration of myofibrillar protein in diaphragm fibers of senescent rats. Isometric twitch and tetanic contractile properties were measured on diaphragm strips from young adult (9-month-old: n = 12) and senescent (26-month-old: n = 13) male specific pathogen free-barrier protected Fischer 344 rats. Maximal tetanic force (Po) normalized to the cross-sectional area (CSA) of the in vitro diaphragm strips was 16.4% lower in the senescent diaphragms (21.03 +/- 0.4 N/cm2) compared to the young adult (25.16 +/- 0.5 N/cm2) (p < 0.001). Diaphragm water content was significantly higher in the senescent group (75.9% of total wet mass) compared to the young adult (72.1% of total wet mass, p < 0.05). Subtracting the contribution of water from the CSA of the diaphragm strips significantly reduced (p < 0.05) the senescent specific Po deficit (from -16.4 to -6.4%). Further, correcting Po for the contribution of myofibrillar protein to CSA resulted in no age group differences in specific force. These data indicate that the age-related decline in diaphragm in vitro maximal specific Po can be explained by an age-related increase in the water content of the diaphragm muscle. Future experiments are necessary to determine the mechanism(s) responsible for this observation.
authors.affiliation: Department of Exercise, University of Florida, Gainesville 32611, USA.
authors.forename: D S
authors.initials: DS
authors.lastname: Criswell
authors.forename: S K
authors.initials: SK
authors.lastname: Powers
authors.forename: R A
authors.initials: RA
authors.lastname: Herb
authors.forename: S L
authors.initials: SL
authors.lastname: Dodd
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001834:Body Water / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D002352:Carrier Proteins; D003964:Diaphragm / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D000099163:Myosin Binding Protein C
chemical_list: D002352:Carrier Proteins; D009124:Muscle Proteins; D000099163:Myosin Binding Protein C