Rapid effects of insulin on in vitro translational activity of specific mRNA in diabetic rat heart

We studied the time course of response of specific cardiac mRNA after administration of insulin to diabetic rats. The primary aim was to identify specific cardiac mRNA, which show a rapid response to insulin administration. Diabetic rats were injected with 2 U of regular insulin intravenously, and total cardiac RNA was prepared 0.5, 1.5, 3, 5, 12, and 24 h later. RNA was translated in vitro in the presence of [35S]methionine and the translational products separated by two-dimensional electrophoresis and quantitated by digital matrix photometry. A rapid change in the translational activity of five specific mRNA species was observed within 0.5 h after administration of insulin to the diabetic animal. One translational product exhibits a more delayed response at 1.5 h. The predominance of three of these products was increased, while that of three was decreased. Two specific mRNA coding for translation products designated as spots 97 and 106 show the most significant change, with a dramatic decrease of 15-fold and 6.5-fold, respectively, within 0.5 h after insulin administration. The change in levels of these specific mRNA species could result from effects of insulin at various sites of mRNA synthesis or degradation. However, the rapidity of the response is compatible with a direct effect of insulin on gene expression. The very quick response of these specific mRNA species to insulin could thus serve as a useful model system to examine the molecular mechanisms of insulin action in the heart.