Manifestation of the stripes of minor proteins location in A-bands of rabbit cardiac myofibrils.

Cardiac myofibrils were isolated from rabbit ventricular muscle by a method that preserves well the integrity of the A-band structure. For the first time electron microscopic observations using the negative staining method revealed, in cardiac A-bands, a full complement of pronounced transverse stripes which indicate the locations of minor proteins in skeletal muscles. The manifestation of some transverse stripes in the cardiac A-band was shown to depend on the duration of muscle incubation in a Ca2(+)-depleting and ATP-free solution before its homogenization into myofibrils. The clear visibility of fine structural details in electron micrographs allowed us to resolve morphological features specific for cardiac muscle at both the central and end parts of the A-bands. The myofibrils demonstrated here are expected to be useful for elucidating the fine structure of cardiac thick filaments and in particular the locations of minor proteins.