N. Safran et al., Cardioprotective effects of adenosine A(1) and A(3) receptor activation during hypoxia in isolated rat cardiac myocytes, MOL C BIOCH, 217(1-2), 2001, pp. 143-152
Adenosine (ADO) is a well-known regulator of a variety of physiological fun
ctions in the heart. In stress conditions, like hypoxia or ischemia, the co
ncentration of adenosine in the extracellular fluid rises dramatically, mai
nly through the breakdown of ATP. The degradation of adenosine in the ische
mic myocytes induced damage in these cells, but it may simultaneously exert
protective effects in the heart by activation of the adenosine receptors.
The contribution of ADO to stimulation of protective effects was reported i
n human and animal hearts, but not in rat hearts. The aim of this study was
to evaluate the role of adenosine A(1) and A(3) receptors (A(1)R and A(3)R
), in protection of isolated cardiac myocytes of newborn rats from ischemic
injury. The hypoxic conditions were simulated by exposure of cultured rat
cardiomyocytes (4-5 days in vitro), to an atmosphere of a N-2 (95%) and CO2
(5%) mixture, in glucose-free medium for 90 min. The cardiotoxic and cardi
oprotective effects of ADO ligands were measured by the release of lactate
dehydrogenase (LDH) into the medium. Morphological investigation includes i
mmunohistochemistry, image analysis of living and fixed cells and electron
microscopy were executed. Pretreatment with the adenosine deaminase conside
rably increased the hypoxic damage in the cardiomyocytes indicating the imp
ortance of extracellular adenosine. Blocking adenosine receptors with selec
tive A(1) and A(3) receptor antagonists abolished the protective effects of
adenosine. A(1)R and A(3)R activation during the hypoxic insult delays ons
et of irreversible cell injury and collapse of mitochondrial membrane poten
tial as assessed using DASPMI fluorochrom. Cardioprotection induced by the
A(1)R agonist, CCPA, was abolished by an A(1)R antagonist, DPCPX, and was n
ot affected by an A(3)R antagonist, MRS1523. Cardioprotection caused by the
A(3)R agonist, Cl-IB-MECA, was antagonized completely by MRS1523 and only
partially by DPCPX. Activation of both A(1)R and A(3)R together was more ef
ficient in protection against hypoxia than by each one alone. Our study ind
icates that activation of either A(1) or A(3) adenosine receptors in the ra
t can attenuate myocyte injury during hypoxia. Highly selective A(1)R and A
(3)R agonists may have potential as cardioprotective agents against ischemi
a or heart surgery.