Molecular mechanisms underlying myocardial hypertrophy induced by ischemia : correlation between changes in intracellular ion concentration and those in expression of immediate-early genes.

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Recent studies have revealed that in many types of cells including cardiac myocytes immediate-early genes (IEG) and/or protein kinase cascade play important roles in recovering or adapting to various stresses or growth stimuli. In order to investigate how cardiac myocytes recover from a brief period of ischemia, we used a metabolic inhibition (MI) model, one of in vitro ischemia models, of chick embryo (10-day-old) ventricular myocytes to examine the induction of c-jun mRNA and the activity of mitogen-activated protein (MAP) kinase. We studied the levels of c-jun mRNA (RNA blot analysis), MAP kinase activity (in-gel kinase assay) and [Ca^<2+>] i (measured with indo-1) during MI using 1 mM sodium cyanide and 20 mM 2-deoxy-d-glucose and also during the recovery from MI.The relative abundance of c-jun mRNA (determined by laser densitometry) remained unchanged during MI of 30 min, but increased significantly during the recovery phase at 30,60,90,120 min (3.0,4.7,2.4,1.9-fold induction as c … More ompared with the pre-MI controls, respectively). When the cells were pretreated with 100 mM of H7, one of the potent protein kinase C inhibitors, the induction of mRNA encoding c-jun at 60 min. during the recovery phase was markedly suppressed (95% reduction of the levelos of c-jun mRNA at 60 min during the recovery without H-7). Pretreatment of the cardiac myocytes with 2 mM EGTA completely inhibited the increase in [Ca^<2+>] i during MI and [Ca^<2+>] i was kept at very lower level (184<plus-minus>26 nM at 30 min. during MI,n=3). This EGTA-pretreatment reduced the levels of c-jun mRNA by 42% (p<0.01, n=3) at 60 min. during recovery from MI of 30 min. as compared with those without EGTA.MAP kinase activity was also unchanged during MI,but significantly increased at 5,10,15 min during the recovery phase (3.0,4.1,3.4-fold increase as compared with the pre-MI controls, respecitively). Thus, these data suggest that IEG c-jun as well as MAP kinase may play significant roles in recovery of cardiac myocytes from a brief period of ischemia. This augmentation of c-jun expression may need the activation of protein kinase C,and to some extent, intracellular Ca^<2+>. Less