Transiently Expressed Proteins In Myocardial Hypertrophy

Pressure overload left ventricular hypertrophy (PLVH) results from an increase in the amount and a shift in isozymic forms of certain contractile proteins. The synthesis of proteins not present in the normal myocardium has not been reported. Total LV RNA was prepared from rat LV, 1, 3, 5, and 7 days after sham operation or PLVH. The [35S] met labelled product of the in vitro translation of the RNA was analyzed by 1 and 2D SDS polyacrylamide gel electrophoresis (SDS PAGE). Both in vivo labelled and total cytoplasmic proteins were similarly analyzed. A 19,5000 MW peptide was synthesized in vitro in PLVH at ld but rapidly disappeared. At 3d, a 42,000 MW peptide appeared in PLVH and gradually diminished by 7d. These peptides were not translated from the SO rat RNA or from RV RNA. These proteins were not present in the in vitro labelled or total proteins from PLVH at any time. These data suggest that species of RNA coding for proteins not normally present in the heart are expressed in PLVH. Although the relative amount of these proteins translated from RNA as judged by the PAGE band intensively is significant, these proteins do not appear in the protein populations of the intact myocardium. This discrepancy in expression suggests that these proteins are either precursor forms or have a regulatory role and are rapidly degraded.