AJP - Heart and Circulatory Physiology, Vol 256, Issue 6 1615-H1620, Copyright © 1989 by American Physiological Society
Effect of ischemia on sarcolemmal Na+-Ca2+ exchange in neonatal hearts
H. Meno, J. M. Jarmakani and K. D. Philipson
Department of Pediatrics, University of California Center for Health Sciences, Los Angeles 90024.
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.
