Vol. 279, Issue 5, H2143-H2150, November 2000
Inhibition of NHE protects reoxygenated
cardiomyocytes independently of anoxic Ca2+ overload and
acidosis
C.
Schäfer,
Y. V.
Ladilov,
M.
Schäfer, and
H. M.
Piper
Physiologisches Institut, Justus Liebig Universität Giessen,
D-35392 Giessen, Germany
We investigated
the question of whether inhibition of the
Na+/H+ exchanger (NHE) during ischemia is
protective due to reduction of cytosolic Ca2+ accumulation
or enhanced acidosis in cardiomyocytes. Additionally, the role of the
Na+-HCO3
symporter (NBS) was
investigated. Adult rat cardiomyocytes were exposed to simulated
ischemia and reoxygenation. Cytosolic pH [2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein
(BCECF)], Ca2+ (fura 2), Na+ [sodium-binding
benzolfuran isophthatlate (SBFI)], and cell length were
measured. NHE was inhibited with 3 µmol/l HOE 642 or 1 µmol/l 5-(N-ethyl-N-isopropyl)-amiloride
(EIPA), and NBS was inhibited with HEPES buffer. During anoxia
in bicarbonate buffer, cells developed acidosis and intracellular Na
and Ca (Nai and Cai, respectively) overload.
During reoxygenation cells underwent hypercontracture (44.0 ± 4.1% of the preanoxic length). During anoxia in bicarbonate buffer,
inhibition of NHE had no effect on changes in intracellular pH
(pHi), Nai, and Cai, but it
significantly reduced the reoxygenation-induced hypercontracture (HOE:
61.0 ± 1.4%, EIPA: 68.2 ± 1.8%). The sole inhibition of
NBS during anoxia was not protective. We conclude that inhibition of
NHE during anoxia protects cardiomyocytes against reoxygenation injury
independently of cytosolic acidification and Cai overload.
hypercontracture; pH control; calcium; sodium-hydrogen exchanger
