Variation of actin filament length in dogs.

As the smallest functional unit of force production, the sarcomeres are important in determining muscle function. Actin filament lengths, which are important in determining optimal sarcomere length for a species, have not yet been reported in dogs. This study aims to provide a species-specific value for actin filament length in dogs, while examining intraspecies, intermuscular and intramuscular variations. Muscle samples were taken from the tibialis anterior muscle, the lateral gastrocnemius muscle head and the medial gastrocnemius muscle head in 10 dogs including a Labrador, a Belgian Malinois, a Caucasian Shepherd, German Shepherds and some mixed-breed dogs. Actin filament lengths were determined through transmission electron microscopy. Mean actin filament length across all muscle samples was 0.90 ± 0.01 μm. The low intraspecies variation, combined with a lack of important inter- and intramuscular variation found in this study, affirms the use of a species-specific optimal sarcomere length of 1.89 μm for canine muscles.