AJP - Cell Physiology, Vol 242, Issue 3 192-C199, Copyright © 1982 by American Physiological Society
Effects of ATP on lysosomes: inhibition of the loss of latency caused by cooling
R. C. Ruth and W. B. Weglicki
Triton-filled lysosomes from rat liver and a crude lysosomal fraction from
livers of rats not injected with Triton have been used to study the ability
of ATP to protect lysosomes against the effects of incubation in vitro at
37 degrees C. When incubation was carried out in a sucrose-NH4Cl medium at
pH 8.0 or in buffer containing 0.15 M KCl at pH 7.4, ATP protected against
the loss of lysosomal enzyme latency that occurred at 37 degrees C and also
against the additional loss of latency that occurred when the incubated
lysosomes were cooled to 0 degrees C. The inhibition of the effects of
cooling was found to result from a decrease in the loss of latency caused
specifically by cooling the lysosomes through the temperature range of the
membrane phase transition (15-0 degrees C); ATP did not affect the basic
rate of loss of latency at 0 degrees C. Protection was minimal when
incubation was carried out in 1 mM ethylenediaminetetraacetic acid without
added divalent metal ion and was enhanced by the addition of either Mg2+ or
Ca2+. Kinetic studies were carried out on the ATP-protective action against
the effects of cooling by adding ATP to lysosomes that had been incubated
at 37 degrees C and that were then cooled to 0 degrees C at various times
after addition of the ATP. Susceptibility to the effects of cooling
continued to decrease until the ATP had been present at 37 degrees C for
approximately 3 min before cooling. The concentration of ATP required for
maximum initial rates of protection was found to be 10(-3) M or possibly
lower. The rate of decrease in susceptibility to the effects of cooling was
much slower when ATP was added at 22 than at 37 degrees C, suggesting that
enzyme action may be involved in the protective mechanism. Possible
mechanisms for the ATP-protective action are discussed.
