Michiko Nojiri (1), Kouichi Tanonaka (1,*), Ken-ichi Yabe (1), Ken-ichiro
Kawana (1), Takeshi Iwai (1), Makiko Yamane (1), Hiroyuki Yoshida (1), Jun-ichi
Hayashi (2) and Satoshi Takeo (1)
(1) Department of Pharmacology, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo 192-0392, Japan
(2) Department of Gerontology, Kyorin University, School of Medicine, Mitaka, Tokyo 181-8611, Japan
(*) To whom all correspondence should be addressed.
Abstract: A possible mechanism for hypoxic preconditioning of adult rat cardiomyocytes was pharmacologically investigated. Isolated cardiomyocytes in all experimental groups were incubated for 120 min under hypoxic conditions followed by 15-min reoxygenation (sustained H/R). Sustained H/R decreased rod-shaped cells, Exposure of the cardiomyocytes to 20-min of hypoxia/30-min reoxygenation (hypoxic preconditioning) attenuated the sustained H/R-induced decrease in rod-shaped cells. The effects of hypoxic preconditioning were abolished by treatment with the protein kinase C (PKC) inhibitor polymyxin B, but abolished by neither the adenosine A1/A2-antagonist sulfophenyl theophylline (SPT) nor the ATP-sensitive potassium channel (KATP channel) blocker glibenclamide. In another series of experiments, cardiomyocytes were incubated without hypoxic preconditioning in the presence of either the PKC activator PMA, adenosine or KATP-channel opener nicorandil and then subjected to sustained H/R. Treatment of the cells with PMA, adenosine or nicorandil mimicked the effects of hypoxic preconditioning. The effects of treatment with adenosine and nicorandil were abolished by polymyxin B treatment. Combined treatment with both SPT and glibenclamide abolished the effects of hypoxic preconditioning, whereas it failed to abolish PMA-induced cytoprotection. These results suggest that the activation of PKC in hypoxic preconditioned cardiomyocytes coupled independently with stimulation of adenosine receptor or opening of KATP channel, either of which is fully enough to exert the cytoprotective effects.
Keywords: Adenosine receptor, Adult rat cardiomyocyte, ATP-sensitive potassium channel, Preconditioning, Protein kinase C