The volume-related activities of sodium ion transporters:
multinuclear nmr studies of isolated rat hearts.
Askenasy, Nadir, and Gil Navon.
School of Chemistry, Tel Aviv University, Tel Aviv 69978,
Israel
APStracts 3:0053H, 1996.
The present study aims to determine the volume-related activities of
sodium ion transporters in the rat heart. Intracellular volumes were
measured in isolated hearts by 1H of water and 59Co NMR of the
extracellular marker cobalticyanide. Inhibition of the Na/K ATPase
pumps with 50 [mu]M ouabain did not affect the extent of cellular
swelling during 30 min of ischemia: cells swelled by 0.37 ml per gram
dry weight (gdw), as compared to the controls (0.38 ml/gdw).
Following perfusion with either 400 [mu]M ouabain or 200 [mu]M
iodoacetate, the cells shrank during ischemia (from 2.50+/-0.06
ml/gdw) to 2.20+/-0.09 and 2.28+/-0.07 ml/gdw, respectively.
Inhibition of passive sodium ion transporters reduced cellular
swelling during ischemia: pretreatment (10 min) with 100 [mu]M
furosemide (Na/K/2Cl cotransport), 1.5 [mu]M ethyl isopropyl
amiloride (EIPA) (Na/H antiport) and 50 [mu]M lidocaine (Na+
channels) led to swelling of 0.27, 0.21 and 0.13 ml/gdw respectively.
The extent of cellular water accumulation was apparently correlated
with the onset and maximal force of the ischemic contracture, unlike
the data of hearts treated with ouabain and iodoacetate. The blockage
of each one of the passive sodium transporters improved the recovery
of intracellular volumes at reperfusion, indicating that in the heart
these pathways are responsible for the sustained reperfusion cellular
edema. It is concluded that acute cellular swelling during myocardial
ischemia is not caused by insufficiency of the Na/K pumps, but is
partially mediated by systems which transport sodium into the cells.
Received 25 September 1995; accepted in final form 2 January
1996.
APS Manuscript Number H906-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96