Pertussis toxin abolishes the cardioprotective effect of ischemic preconditioning in intact rat heart.

It has been previously demonstrated that Gi/o proteins are involved in ischemic preconditioning (IPC) in rabbits and dogs; however, there has been controversy as to the role of Gi/o proteins in IPC in in vivo rat infarct models. Therefore, the role of G proteins in the cardioprotective effect of IPC in a rat infarct model was reevaluated. Cardioprotection as indicated by infarct size (IS) as a percentage of the area at risk (IS/AAR) was determined by triphenyltetrazolium stain. The control group, which was subjected to 30 min of occlusion (Occ) and 2 h of reperfusion (Rep), had an IS/AAR of 46 +/- 6%. A single 5-min Occ followed by 10 min of Rep (1x PC) as well as three 5-min Occ periods interspersed with 5 min of Rep (3x PC) markedly reduced IS/AAR (6 +/- 1 and 8 +/- 1%, respectively). Pretreatment with pertussis toxin (10 microg/kg ip) for 48 h before 1x PC or 3x PC completely abolished their cardioprotective effects (46 +/- 5 and 38 +/- 4%, respectively). Pertussis toxin had no effect on IS/AAR and did not inactivate Gi/o proteins as assessed by an in vitro ADP-ribosylation assay of heart homogenates. These results demonstrate that the cardioprotective effect of IPC is mediated by a small subpopulation of Gi/o proteins in the intact rat heart.