Seasonal variation in the phenotype of adult ferret (Mustela putorius furo) cremaster muscle.

Using immunocytochemistry, electrophoresis and immunoblotting, we studied the expression of fast and slow myosin heavy chain isoforms in adult ferret muscles during quiescent and breeding periods. Adult cremaster muscle expressed slow and fast myosin heavy chain in relatively similar amounts during the quiescent period. During the breeding period, the expression of slow myosin heavy chain, I, significantly decreased, and fast myosin heavy chain II, was predominant.