In the goat ischaemic preconditioning (IP) reduces the total hyperaemic flow (THF) of a coronary reactive hyperaemia (CRH) obtained with a 15 s occlusion of the left circumflex coronary artery (LCCA) (Pagliaro et al. 2001). This study aimed to investigate whether the reduction of THF by IP is related to an impairment of ATPase activity by F0F1 ATP synthase by binding of its inhibitory protein IF1. The experiments were performed on six anaesthetised goats ventilated with a 2:1 gaseous mixture of nitrous oxide and oxygen. After sedation with diazepam (40 mg) anaesthesia was induced by I.V. injection of ketamine (15 mg kg-1), and maintained by infusion of ketamine and hourly injection of 2.5 ml of fentanyl.
Aortic blood pressure and flow in the LCCA were recorded. CRH was induced before and after IP by a 5 min occlusion of the artery. Myocardial samples were taken in the absence and in the presence of preconditioning before, during and after each CRH. In particular, during CRH, samples were taken 15Ð20 s after the release of the occlusion, i.e. at the top of the hyperaemia, and after CRH was over, i.e. 4 and 6 min after the release. ATPase activity and IF1 content in ATP synthase were determined in all samples. Mean ± S.D. data were analysed by Student’s t test for paired data. P < 0.05 was considered significant. Animals were humanely killed.
In the non-preconditioned heart, ATPase activity was 1.0 ± 0.13 U (mg total protein)-1 before CRH, while it became 1.2 ± 0.15 at the top of CRH, and 0.76 ± 0.14 U mg-1 4 min after the release of the 15 s occlusion of LCCA. After 6 min had elapsed from the release, ATPase activity was back to the control value (0.97 ± 0.1 U mg-1).
After IP, CRH showed a significant (P < 0.005) 24 % decrease of THF from 164 ± 45 to 124 ± 27 ml. At the same time ATPase activity was reduced to 0.86 ± 0.16 U mg-1 before CRH. At the top of the hyperaemia it was 1.0 ± 0.06 U mg-1 and back to the control (0.88 ± 0.12 U mg-1) 4 min after the release of the 15 s occlusion of LCCA. It is noticeable that the mean value of ATPase activity at the top of CRH after preconditioning was significantly lower than the corresponding value obtained before IP. Furthermore, the value of ATPase activity observed 4 min after the release of the 15 s occlusion of LCCA ATPase activity was not significantly different from the control while before preconditioning the corresponding value was significantly lower, indicating that modulation of F0F1ATPsynthase was due to the binding and release of F1. Finally a negative linear correlation has been found between ATPase activity and IF1 content (IF1/F1 ratio).
It may be concluded that, after IP, the reduction of THF could match the down-modulation of ATPase activity mediated by the binding of its specific inhibitory protein IF1.
We thank the ‘Compagnia di San Paolo’ and MIUR (Cofin 2000).
All procedures accord with current local guidelines.