Myosin heavy chain composition of adult feline (Felis catus) limb and diaphragm muscles.

The myosin heavy chain (MHC) compositions of adult feline limb and diaphragm muscles were determined. Sodium dodecyl sulfate-polyacrylamide gels (SDS-PAGE) were able to separate three different MHC isoforms. This was in contrast to rat muscles, in which four MHC isoforms were separated by SDS-PAGE. The fastest migrating cat MHC migrated similar to rat type I MHC and labeled in Western blots with a monoclonal antibody (mAb) specific for slow MHC and was categorized as type I. The other two MHC isoforms labeled in Western blots with a mAb specific for fast MHC and were categorized as type II. The slowest migrating fast isoform migrated similar to rat type IIa MHC and labeled with mAb N2.261, specific for types I and IIa; therefore, this MHC was categorized as type IIa. The intermediate migrating cat MHC did not migrate similar to either rat type IIx or type IIb and was not reactive with mAbs N2.261, 35 (specific for rat I, IIa, and IIb MHCs), or F3 (specific for rat IIb MHC). In tissue sections, type IIB fibers (based on myofibrillar ATPase histochemistry) were also unstained with mAbs N2.261 and 35. Therefore, the intermediate migrating cat MHC was categorized as type IIx. Consequently, feline limb and diaphragm muscles were composed of fibers containing type I, IIa, or IIx MHCs. The observations that type I and IIa isoforms, but not IIx, had similar electrophoretic mobilities in the cat and rat and that type IIb was absent from cat limb muscles suggest that there is greater diversity in MHC isoforms IIb and IIx compared to I and IIa in cats compared to rats.