Myosin isoenzyme distribution in striated muscle of cocaine-conditioned rats

While cocaine treatment alters the myosin phenotype in slow type striated muscle, it remains unknown whether the myosin phenotype of other types of striated muscles are similarly impacted. To make this determination, male Sprague-Dawley rats were injected ip. twice daily with either saline or cocaine (12.5 mg/kg). After 15 days the heart, diaphragm, and tibialis anterior (TA) muscles were removed. Myofibrils were isolated from these muscles and electrophoretically separated into their respective isoforms under nondenaturing conditions and into their heavy chain components under denaturing conditions (diaphragm, TA). This cocaine treatment regimen did not alter the myosin isoform composition or the myosin heavy chain components of any of these muscles. Because cocaine does alter the myosin isoenzyme profile of the soleus muscle, these findings suggest that cocaine selectively impacts slow skeletal muscle.