The effects of Suramin on Ca 2+ activated force and sarcoplasmic reticulum Ca 2+ release in skinned fast‐twitch skeletal muscle fibers of the rat

Suramin has long been used in the treatment of various human diseases. Intravenous infusions of Suramin are commonly administered to patients over extended periods of time but there are a number of significant contraindications with peripheral muscle weakness being one of the most frequently reported. Previous work has shown that even after a single infusion (300 mg kg −1 ) Suramin remains in skeletal muscle in effective concentrations (11.6  μ g  mL −1 ; 84 days) for prolonged periods. These observations provide a strong rationale for investigation of the specific effects of Suramin on skeletal muscle function. Single mechanically skinned fibers were directly exposed to Suramin (10, 100 or 500  μ mol L −1 ) for defined durations (2–10 min) in controlled physiological solutions that mimic the intracellular ionic environment of a fiber. Suramin treatment (10–500  μ mol L −1 ) directly affected the contractile apparatus in a dose‐dependent manner causing a decrease in Ca 2+ ‐sensitivity ( pC a50 = −log (Ca 2+ ) concentration, where 50% of maximum Ca 2+ ‐ activated force is produced) by 0.14 to 0.42 pC a units and reduction in maximum Ca 2+ ‐activated force by 14 to 62%. Suramin treatment (100  μ mol L −1 for 10 min and 500  μ mol L −1 for 2 min) also caused development of a Ca 2+ ‐independent force corresponding to 2.89 ± 4.33 and 16.77 ± 7.50% of pretreatment maximum Ca 2+ ‐activated force, respectively. Suramin treatment (100  μ mol L −1 , 2 min) also increased the rate of sarcoplasmic reticulum ( SR ) Ca 2+ release without significant changes in SR Ca 2+ uptake. We report new functional effects for Suramin related to alterations in both the contractile apparatus and SR Ca 2+ ‐handling of skeletal muscle that may contribute to the peripheral muscle weakness noted in human pharmacological treatments.