Cardiomyocyte
sodium accumulation after
burn injury precedes the development of myocardial contractile dysfunction. The present study examined the effects of
burn injury on Na-K-
ATPase activity in adult rat hearts after major
burn injury and explored the hypothesis that
burn-related changes in myocardial Na-K-
ATPase activity are PKC dependent. A third-degree
burn injury (or
sham burn) was given over 40% total body surface area, and rats received
lactated Ringer solution (4 ml.kg(-1).%
burn(-1)). Subgroups of rats were killed 2, 4, or 24 h after
burn (n = 6 rats/time period), hearts were homogenized, and Na-K-
ATPase activity was determined from
ouabain-sensitive
phosphate generation from
ATP by cardiac sarcolemmal vesicles. Additional groups of rats were studied at several times after
burn to determine the time course of myocyte
sodium loading and the time course of myocardial dysfunction. Additional groups of
sham burn-injured and
burn-injured rats were given
calphostin, an inhibitor of PKC, and Na-K-
ATPase activity, cell Na(+), and myocardial function were measured.
Burn injury caused a progressive rise in cardiomyocyte Na(+), and myocardial Na-K-
ATPase activity progressively decreased after
burn, while PKC activity progressively rose. Administration of
calphostin to inhibit PKC activity prevented both the
burn-related decrease in myocardial Na-K-
ATPase and the rise in intracellular Na(+) and improved postburn myocardial contractile performance. We conclude that
burn-related inhibition of Na-K-
ATPase likely contributes to the cardiomyocyte accumulation of intracellular Na(+). Since intracellular Na(+) is one determinant of electrical-mechanical recovery after insults such as
burn injury,
burn-related inhibition of Na-K-
ATPase may be critical in postburn recovery of myocardial contractile function.