Insights into the cardioprotective function of adenosine A(1) and A(3) receptors.

OBJECTIVES: Cardioprotection (delaying of irreversible damage in hypoxia or prevention of doxorubicin [DOX] toxicity) is achieved by increasing the energy supply, or decreasing the energy demand in the cell and may be regulated through adenosine (ADO) receptor (AR) signalling. The aim of this study was to define of the protective role of ADO A(1)R and A(3)R against these two different kinds of stress conditions via direct action on isolated cardiomyocytes. Effects of A(1) and A(3) adenosine receptors were assessed by comparing morphological-functional tolerance, cellular energy state and contribution of the mitochondrial K(ATP) channels during development of hypoxia and DOX cytotoxicity.
METHODS: The primary cardiac myocyte cultures were treated in a hypoxic chamber of N(2) (100%) in glucose-free media. A second group of cells were treated on day 4 in culture with 0.5 to 5 muM DOX for 18 h and then incubated in drug-free growth medium for an additional 24 h or 72 h. The hypoxic and cytotoxic damage was characterized by morphological and biochemical evaluations.
RESULTS: The A(1)R and A(3)R selective agonists (CCPA and Cl-IB-MECA, respectively) significantly decreased damage to cardiac myocytes under hypoxic conditions. Activation of both A(1)R and A(3)R together (100 nM) was more efficient in protection against hypoxia than by each one alone. The A(3)R agonist Cl-IB-MECA (100 nM) shows cardioprotective activity to the DOX-treated cells; however, the A(1)R agonist CCPA (10 nM to 10 muM) was not effective in protection against DOX toxicity.
CONCLUSION: Activation of both the ADO receptors (A(1)R and A(3)R) leads to positive beneficial effects in cultured cardiomyocytes in 90 min hypoxia, but only A(3)R activation renders positive response against slowly developed DOX toxicity. Hence, the cascade of events involved in cardioprotection appears to be distinct for A(1) and A(3) receptor signalling.