AJP - Heart and Circulatory Physiology, Vol 248, Issue 3 345-H349, Copyright © 1985 by American Physiological Society
Low sodium attenuation of the Ca2+ paradox in the newborn rabbit myocardium
S. Uemura, H. Young, S. Matsuoka and J. M. Jarmakani
The effect of low sodium (Na 24 mM) perfusate during Ca2+ depletion on
mechanical function, tissue high-energy phosphate, creatine kinase (CK)
release, and tissue potassium was studied in the arterially perfused
newborn and adult rabbit heart. During Ca2+ depletion, the time for DT and
+dT/dtmax to decline to half-maximal value in newborn muscles perfused with
low Na (46 +/- 3 S) was significantly (P less than 0.05) longer than the
value obtained with normal Na (14 +/- 1 S). Similar values were obtained in
the adult. During Ca2+ repletion, the increase in resting tension and CK
release was attenuated in the low Na groups, and the values in the newborn
were significantly less than in the adult. The recovery of +dT/dtmax and
tissue high-energy phosphates in the low Na groups were significantly
greater than in the normal Na groups, and the values in the newborn were
significantly greater than in the adult. These data suggest that low Na
during the Ca2+-free period delays both cellular Ca2+ depletion during the
Ca2+-free period and Ca2+ influx during Ca2+ repletion. This effect in the
newborn is greater than in the adult and might be explained by Na+-Ca2+
exchange.
