Abstract
Electrode measurements were made of the free Ca2+ concentration maintained by suspensions of isolated rat liver mitochondria and microsomes, as well as by hepatocytes whose plasma membranes had been made permeable by treatment with digitonin. When the KCl, ATP, Mg2+, and phosphate concentrations were made similar to that of cytosol, the steady state free Ca2+ concentration in the presence of respiring mitochondria alone was about 0.5 microM. The additional presence of rat liver microsomes resulted in a steady state level of close to 0.2 microM, which was maintaied for greater than 1 h at 25 degrees C. This concentration of Ca2+ was also maintained by suspensions of hepatocytes permeabilized by digitonin and thus may approximate the actual cytosolic free Ca2+ concentration in vivo. The "set point" for free Ca2+ homeostasis in these systems is determined by mitochondrial Ca2+ influx-efflux cycling, which is dependent on the level of intramitochondrial Ca2+ and can be adjusted by sequestration of Ca2+ in microsomes.
Highlights
From the Department of Physiological Chemist?, The Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205 tions close to those in the cell cytosol have been evaluated and compared to values for the free Ca2+concentration maintained by suspensions of rat hepatocytes whose plasma membranes have been made selectively permeable to ions and Electrode measurements were made of the free Ca2m+olecules by treatment with low concentrations of digitonin concentration maintained by suspensions of isolated (10, 14, 15)
Liver microsomeswere prepared in a medium rat liver microsomes resultedin a steadystate level of close to 0.2 p ~w,hich was maintained for greater than 1 h at 26°C.T h i s concentration of Ca2+ waaslso maincontaining 250 mM sucrose, 1 mM EGTA/Tris by centrifugation of the postmitochondrial supernatant fraction at 100O, OO X g (30 min)
Hepatocytes for free Ca2+ homeostasis in these systems is deter- were isolated by the collagenase-hyaluronidase perfusion method minedbymitochondrial Ca" influx-effluxcycling, which is dependent on the level of intramitochondrial
Summary
Dria the addition of rat liver microsomes caused significant As shown in Fig. lC,when isolated rat hepatocytes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
