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