AJP - Heart and Circulatory Physiology, Vol 252, Issue 1 32-H39, Copyright © 1987 by American Physiological Society
Deinhibition of cardiac Na+-K+-ATPase after exposure to exogenous phospholipase A2
R. A. Colvin
After 2 h of exogenous phospholipase A2 (PLA2) exposure, membrane
phospholipid decreased from 3.22 +/- 0.31 to 1.06 +/- 0.13 mumol/mg (33% of
control). All classes of phospholipid, except sphingomyelin, were
hydrolyzed, whereas total cholesterol content was unaffected. Increases in
nonesterified fatty acids (NEFA) were reflected primarily in oleic (18:1),
linoleic (18:2), and arachidonic (20:4). Na+-K+-adenosinetriphosphatase
(ATPase) activity was inhibited to 29% of control by 2 h of PLA2 treatment,
and this inhibition was reversed (albeit, not completely after 5 min of
PLA2 treatment) by removal of the hydrolysis products with 0.1% bovine
serum albumin (BSA). In contrast, the apparent binding capacity for
[3H]ouabain was not affected by PLA2 treatment. Unmasking of latent
[3H]ouabain binding by alamethicin was utilized to estimate changes in the
proportion of sealed vesicles present before and after PLA2 treatment. PLA2
treatment resulted in a time-dependent loss of sealed vesicles that
paralleled the time course of phospholipid hydrolysis and was not reversed
by washing with BSA. These studies demonstrate that cardiac Na+-K+-ATPase
activity is inhibited by accumulation of endogenously produced
lysophospholipids and NEFA. In contrast, loss of vesicle integrity may
result from both accumulation of endogenously produced hydrolysis products
and membrane phospholipid depletion.
