AJP - Heart and Circulatory Physiology, Vol 249, Issue 1 20-H28, Copyright © 1985 by American Physiological Society
Response of canine cardiocyte lysosomes to ATP
A. M. Spanier, B. F. Dickens and W. B. Weglicki
The present study was designed to evaluate the relationship of adenosine
triphosphate (ATP) to maintenance of cardiac lysosome latency. Highly
latent lysosomes were isolated from adult canine ventricular myocytes or
cardiocytes and exhibited latency values (based on % free
N-acetyl-beta-glucosaminidase, NAGA) of 29.3 +/- 4.7% (SE), minimal cross
contamination by mitochondria (less than 2% cardiolipin by weight) and only
1.68% of the total cytochrome c oxidase activity; enzymatic enrichments
ranged from 10-fold for NAGA to almost 50-fold for cathepsin B. Incubations
of cardiocyte lysosomes at pH 7.0 and 25 degrees C for up to 1 h resulted
in changes in the rate of loss in lysosomal latency when ATP levels were
adjusted from 0.0 to 5.0 mM; under these conditions as ED50 of 0.62 mM ATP
was determined. The protection afforded by ATP was reversed by addition of
the H+ ionophore m-chlorocarbonylcyanide phenylhydrazone (CCCP) at 10
microM to the lysosomal suspensions. A significant increase in lysosomal
membrane fluidity, measured by fluorescent polarization of
diphenylhexatriene, was also seen in the absence of ATP. Adenosine
diphosphate (ADP) afforded significant protection only at the very highest
concentration (5.0 mM); inorganic pyrophosphate (PPi) did not protect
against loss of latency at any concentration. Thus ATP exerts a significant
stabilizing effect on cardio(myo)cyte lysosomes in vitro and may be one of
the metabolites regulating lysosomal integrity in vivo.
