Hormonal induction of c-fos and HSP68 mRNAs on an isolated coronary perfused adult rat heart.

Transient growth signals which can be related to protein synthesis and cellular growth are of particular interest in the heart because of the incidence of cardiac hypertrophy in man. The isolated coronary perfused adult rat heart or the so-called Langendorff preparation, is an useful model in exploring not only protein synthesis but also c-fos/c-myc protooncogene and Heat Shock Protein (HSP) gene expression. Phenylephrine infusion in this preparation induces c-fos expression whether the heart is beating or reversibly or irreversibly arrested by solutions enriched in KCl. Norepinephrine has the same effect. Quantitative analysis with slot blots shows that in both cases the adrenergic effect has a dual origin since it is inhibited both by propranolol, a beta-adrenergic antagonist, and terazosine, a soluble alpha 1-adrenergic antagonist. We conclude that the isolated heart is a useful tool to explore the early changes in gene expression which occur in this tissue in response to various physiological stimuli.

Experimental systolic and diastolic overloading in rats: total proteins turnover rate. Enzymatic and structural properties of myosin.

The fractional turnover rate of the total cardiac proteins has been measured by using the continuous infusion technique with 3H lysine. It augments by a factor of 3 in systolic as well as in diastolic overloading, but in the former the peak was reached within the first week after operation and in the later the peak was not reached until the 14th day. The myosin structure and enzymatic properties have been studied in several huge hypertrophic hearts (around 100% hypertrophy). In this condition the burst size of myosin is normal, as well as its K+ ATPase, but there is a sharp decline in the Ca2+ ATPase activity. Moreover, antibodies against native or defolded heavy meromyosin exhibit, a vertical shift in microcomplement fixation when made to react with molecules extracted from hypertrophied hearts. The normal isozymic pattern of rat heart myosin, as shown in non dissociating electrophoresis, was reversed.

Comparative study of two ATP : L-arginine phosphotransferases of molecular weight 84 000.

Solen ensisensis muscle arginine kinase (ATP : L-arginine phosphotransferase, EC 2.7.3.3) was isolated in an homogeneous state. Its molecular weight was found to be about 80 000. The properties of this enzyme were compared with those of arginine kinase from Sipunculus nudus, an enzyme which also has a molecular weight of about 80 000. Both enzymes have several reactive thiol groups (8 thiol groups in the Solen kinase and 12 in the Sipunculus enzyme were titrateable with 5,5'-dithio-bis-(2-nitrobenzoic) acid and histidine residues (both enzymes have 6 reactive histidine residues). These kinases were, therefore, highly susceptible to oxidation. Both enzymes show the same pH optimum and absolute specificity towards the guanidine substrate, L-arginine. The reaction kinetics of both enzymes are of the sequential type. In the presence of alpha-aminoacids of Mg2+-ADP, similar spectral effects were obtained. The enzymes differ in their enzymic activities and in their rate of recovery following urea denaturation. The most important difference that appeared to be a special feature of the Sipunculus enzyme is that the spectrum of the Mg2+-ADP-enzyme complex is strongly intensified by L-arginine.