Functional properties of skinned rabbit skeletal and cardiac muscle preparations containing a-cardiac myosin heavy chain

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Abstract
Contractile properties of skinned muscle fibres from the masseter muscle and strips of heart atrium muscle from rabbits, both containing the α-cardiac myosin heavy chain isoform (α-cardiac MHC), were investigated and compared with those of other skeletal muscle fibre types. The stretch-induced delayed force increase (stretch activation) was investigated on maximally Ca2+-activated skinned preparations as an index of the kinetic properties of the myosin heads of various MHC isoforms. Skeletal muscle fibres containing exclusively α-cardiac MHC (type α) and muscle strips of heart atrium showed specific kinetics of stretch activation intermediate between those of types IIA and I fibres. In agreement with available data the unloaded shortening velocity V u of type α fibres was also intermediate between that of types IIA and I fibres. Compared with skeletal muscle type α fibres, muscle strips of heart atrium exhibited significantly (PIID(X)>IIA>α>I.