Corticosteroid effects on isotonic contractile properties of rat diaphragm muscle

Abstract

Van Balkom, Roland H. H., Wen-Zhi Zhan, Y. S. Prakash, P. N. Richard Dekhuijzen, and Gary C. Sieck. Corticosteroid effects on isotonic contractile properties of rat diaphragm muscle. J. Appl. Physiol. 83(4): 1062–1067, 1997.—The effects of corticosteroids (CS) on diaphragm muscle (Dia m ) fiber morphology and contractile properties were evaluated in three groups of rats: controls (Ctl), surgical sham and weight-matched controls (Sham), and CS-treated (6 mg ⋅ kg −1 ⋅ day −1 prednisolone at 2.5 ml/h for 3 wk). In the CS-treated Dia m , there was a selective atrophy of type IIx and IIb fibers, compared with a generalized atrophy of all fibers in the Sham group. Maximum isometric force was reduced by 20% in the CS group compared with both Ctl and Sham. Maximum shortening velocity in the CS Dia m was slowed by ∼20% compared with Ctl and Sham. Peak power output of the CS Dia m was only 60% of Ctl and 70% of Sham. Endurance to repeated isotonic contractions improved in the CS-treated Dia m compared with Ctl. We conclude that the atrophy of type IIx and IIb fibers in the Dia m can only partially account for the CS-induced changes in isotonic contractile properties. Other factors such as reduced myofibrillar density or altered cross-bridge cycling kinetics are also likely to contribute to the effects of CS treatment.