Decreased accumulation of β 1-adrenergic receptor, Gαs and total myosin heavy chain messenger RNAs in the left ventricle of senescent rat heart

Abstract

The expression of genes coding for the β 1-adrenergic receptor (β 1-AR), the α subunit of Gs and total myosin heavy chain (MHC) was compared between left ventricles (LV's) from young (6–7 weeks old) and old (22 months old) rats. The mRNA levels were quantitated by Northern or Slot blots analyses using specific DNA probes. Ageing was found to be associated with a reduction in β1-AR (77%), Gαs (33%) and total MHC (51%) mRNA levels with no concomitant change in 18S RNA and poly(A +) mRNA levels. These results indicate that transcriptional and/or post-transcriptional mechanisms participate in the control of β-adrenergic receptor density during ageing. As in the senescent LV, β 1-AR mRNA level is reduced in the hypertrophied LV, whereas the level of Gαs mRNA is reduced in the senescent but not in the hypertrophied LV. From our data we conclude (1) that a dual mechanism may operate during ageing, mechanical factors indirectly regulating β 1-AR mRNA level, while changes in Gαs mRNA level do not depend on hemodynamic load and (2) that the re-expression of β-MHC mRNA does not compensate for the decreased accumulation of α-MHC mRNA which results in a large decrease in the level of total MHC mRNA in the senescent LV.