Effect of hypothermic cardioplegia on cardiac protection--I. Effect of hypothermic cardioplegia on the cytosolic Ca2+ concentration in rat ventricular myocytes.
Cytosolic Ca2+ concentration of rat ventricular cells was measured under varying experimental conditions by using a fluorescent Ca2+ indicator, Fura-2. Resting [Ca2+]i of rat myocyte was 150 +/- 30 nM (n = 39), and this value was compatible with others. The Perfusion of cardioplegic solution significantly increased [Ca2+]i, and this effect was further augmented by hypothermia (p < 0.05). Application of nifedipine (5 x 10(-7) M) to the perfusate or pretreatment of caffeine (10 mM) had no apparent effect on this cardioplegia-induced [Ca2+]i change. But Ni2+ (5 mM), an antagonist of Na+/Ca2+ exchange mechanism, prevented the [Ca2+]i change during cardioplegia (p < 0.05). Magnitude of cardioplegia-induced [Ca2+]i increase was also dependent on the Ca2+ concentration of cardioplegic solution. These results suggest that Na+/Ca2+ exchange may play an important role in cardioplegia-induced [Ca2+]i change. To rule out the possibility whether the protective effect of hypothermic cardioplegia is due to the preservation of high-energy phosphate store or decreasing the transmembrane ionic fluxes by phase transition, we exhausted a energy store of cardiac cell by application of 2,4 dinitrophenol to the bath and measured its effect on [Ca2+]i change during cardioplegia. Hypothermic cardioplegia delayed the onset of [Ca2+]i increase and decreased its amplitude compared to those of normothermic cardioplegia. From the above results, hypothermic cardioplegia may protect the cardiac cells from ischemic insult by preserving a high-energy phosphate store. Application of Ni2+ to the cardioplegic solution or reduction of external Ca2+ concentration also had some protective effect, since it prevented [Ca2+]i increase during cardioplegia.
Ahn
D S
DS
Yonsei University College of Medicine, Department of Physiology, Seoul, Korea.
Lee
Y H
YH
Kang
D H
DH
Kang
B S
BS
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006324:Heart Arrest, Induced; D006352:Heart Ventricles / Q000378:metabolism; D007036:Hypothermia, Induced; D017202:Myocardial Ischemia / Q000378:metabolism / Q000517:prevention & control*; D009206:Myocardium / Q000378:metabolism*; D051381:Rats
D002118:Calcium