VARIATIONS IN THE RELATIVE MESSENGER-RNA LEVELS OF ACTINS AND MYOSIN HEAVY-CHAINS DO NOT PRODUCE CORRESPONDING DIFFERENCES IN THEIR PROTEINS IN THE ADULT HUMAN HEART

This paper examines the quantitative relationship between the expressi on of myosin heavy chain (MHC) and actin at both the levels of their m RNAs and their proteins. Explanted human left ventricle tissues were o btained from non-diseased (ND) individuals and from dilated cardiomyop athy (DCM) patients with terminally failing hearts who underwent heart transplantation. We found: ii) there are substantial differences in t he stoichiometry of sarcomeric MHC and actin transcripts in hearts of DCM patients as well as in ND individuals; (2) there are substantial d ifferences between levels of total sarcomeric actin transcripts from d ifferent individual patients; (3) by and large variations in transcrip t levels between samples from the same heart are much less than betwee n samples from different hearts: and (4) the ratio of MHC to sarcomeri c actin proteins expressed by different ND and DCM hearts remains esse ntially constant. We conclude that the human ventricle can accomodate a substantial imbalance between sarcomeric MHC and actin mRNA levels w hile maintaining a constant ratio of their corresponding proteins. (C) 1997 Academic Press Limited.