Time course analysis of cardiac pacing-induced gene expression changes in the canine heart.

Rapid right ventricular pacing in anesthetized dogs results in marked protection against ischemia and reperfusion-induced ventricular arrhythmias, 24 h later. We have previous evidence that this protection associates with altered expression of genes, encoding proteins involved in the delayed cardioprotection. However, the sequence of transcriptional changes occurring between the pacing stimulus and the test ischemia has not yet been elucidated. Thus, we designed studies in which the expression of 29 genes was examined by real-time PCR at various time intervals, i.e., immediately (0 h), 6, 12, and 24 h after short periods (4 times 5 min) of rapid (240 beats min(-1)) right ventricular pacing in the canine. Sham-operated dogs (the pacing electrode was introduced but the dogs were not paced) served as controls. Compared with these dogs, pacing induced an early up-regulation of genes which encode, for example, HSP90, MnSOD, ERK1, PKCε, Bcl2, and sGC; all these somehow relate to the early phase of the protection. These genes remained either up-regulated or, after a transient lower expression (around 6 h), were up-regulated again, suggesting their involvement in the delayed protection. There were also some genes which down-regulated soon after the pacing stimulus (e.g., Bax, Casp3, Casp9, MMP9, GSK3β), and showed also low expression 24 h later. Genes encoding eNOS and iNOS, as well as Cx43 were only up-regulated 12 h after pacing. We conclude that cardiac pacing induces time-dependent changes in gene expression, and the sequence of these changes is important in the development of the delayed protection.