title: Effect of ischemia on sarcolemmal Na+-Ca2+ exchange in neonatal hearts.
abstract: We studied the effect of cardiac ischemia on sarcolemmal enzymes, Na+-Ca2+ exchange, Ca2+ binding, and Ca2+ efflux in the newborn and adult rabbit. Rabbit ventricle was made ischemic by incubation in hypoxic, glucose-free Tyrode solution at 37 degrees C for 60-120 min. Ischemia inhibited Na+-K+-ATPase and K+-p-nitrophenylphosphatase (PNPPase) activity in the adult myocardium more than in the newborn. In the oxygenated (control) hearts, Na+-Ca2+-exchange activity in the newborn sarcolemma [Michaelis constant (Km) 18 microM; maximum velocity (Vmax) 33] was similar to that in the adult (Km = 16 microM, Vmax = 32). After 60 min ischemia, however, Na+-Ca2+ exchange in the newborn (Km = 16 microM, Vmax = 18) was inhibited less than in the adult (Km = 25 microM, Vmax = 18). In the two age groups, Ca2+ binding and efflux rate were not increased after ischemia, which suggested that Ca2+ permeability did not increase during ischemia. In conclusion, ischemia inhibited sarcolemmal enzymes and Na+-Ca2+ exchange in the newborn less than in the adult, and this lesser inhibition might contribute to or be caused by the greater tolerance of the newborn heart to ischemia.
authors.affiliation: Department of Pediatrics, University of California Center for Health Sciences, Los Angeles 90024.
authors.forename: H
authors.initials: H
authors.lastname: Meno
authors.forename: J M
authors.initials: JM
authors.lastname: Jarmakani
authors.forename: K D
authors.initials: KD
authors.lastname: Philipson
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism; D003327:Coronary Disease / Q000201:enzymology*; D006321:Heart / Q000254:growth & development; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D011817:Rabbits; D012508:Sarcolemma / Q000201:enzymology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D000251:Adenosine Triphosphatases; C034688:sodium calcium ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium