[Role of the Na+/H+ pump in heart ischemia-reperfusion lesions in the neonatal period].
OBJECTIVE
Amiloride 5-(N,N-dimethyl)(AMD), an Na+/H+ pump inhibitor, was used to evaluate the maturity and sensitivity of the Na+/H+ pump in neonatal myocardial cells.


METHODS
Using the isolated contraction isometric heart model, the hearts of neonatal rabbits (10-12 days) were stopped by cardioplegia with and without AMD (20 mumoles/l), then submitted to 40 minutes of ischaemia at 37 degrees C or 120 minutes of ischaemia at 20 degrees C before being reperfused for 30 minutes at 37 degrees C. When AMD was added to the cardioplegic solution, it was also added (20 mumoles/l) to the Krebs solution for the first five minutes of reperfusion. Functional assessment of myocardial contractility and relaxation was performed before aortic clamping and after 30 minutes of reperfusion. Coronary venous drainage during reperfusion was collected to evaluate CPK levels.


RESULTS
To 37 degrees C or 20 degrees C, Na+/H+ pump inhibition was marked by improvement of all myocardial contractility and relaxation parameters at the end of the reperfusion period. A significantly reduced CPK release wase also observed during reperfusion associated with Na+/H+ pump inhibition.


CONCLUSIONS
This study demonstrates maturation of the Na+/H+ pump in neonatal myocardial cells and confirms the role of this ion exchange pump in the pathogenesis of ischaemia-reperfusion lesions. The study at 20 degrees C demonstrated the sensitivity of the Na+/H+ pump to a low transmembrane proton gradient.
Baron
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Service de Chirurgie cardiaque, Hôpital G. et R. Laënnec, bd J. Monod, BP 1005, 44093 Nantes.
Rebeyka
I M
IM
D000367:Age Factors; D000584:Amiloride / Q000032:analysis / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001794:Blood Pressure; D002314:Cardioplegic Solutions / Q000737:chemistry; D003326:Coronary Circulation; D003402:Creatine Kinase / Q000097:blood; D004195:Disease Models, Animal; D006324:Heart Arrest, Induced / Q000379:methods; D006339:Heart Rate; D007552:Isotonic Solutions / Q000737:chemistry; D009200:Myocardial Contraction; D015428:Myocardial Reperfusion Injury / Q000209:etiology* / Q000378:metabolism* / Q000503:physiopathology; D011817:Rabbits; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000502:physiology*; D013997:Time Factors; D017725:Ventricular Pressure
D002314:Cardioplegic Solutions; D007552:Isotonic Solutions; C051865:Krebs-Ringer solution; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D003402:Creatine Kinase