Canine corticosteroid-induced alkaline phosphatase in serum was
solubilized by phospholipase activity in vivo.
Hoffmann, Philip F. Solter Walter E.
University of Illinois at Urbana-Champaign, College of Veterinary
Medicine, Department of Pathobiology, 2001 South Lincoln Avenue,
Urbana, IL 61801
APStracts 2:0058G, 1995.
In this study, gas chromatography/mass spectrometry revealed the
presence of stoichiometric amounts of myo-inositol in association
with serum corticosteroid-induced isoenzyme of alkaline phosphatase
(CALP) in canine serum. Such remnants are consistent with prior
membrane attachment of serum CALP and its release into serum by
endogenous phospholipase activity. Serum CALP was further shown to
behave similarly to CALP released from hepatocyte membranes by
glycosyl phosphatidylinositol phospholipase D (GPI-PLD) and
differently from CALP solubilized by GPI-PLC on both native
polyacrylamide gel electrophoresis and Western blot analysis using
anti-cross reacting determinant antibody. In addition to bile
canalicular surfaces, CALP activity was found over hepatocyte
sinusoidal surfaces by histochemical staining of canine liver
sections. A significantly higher ratio of CALP to total alkaline
phosphatase activity was observed in serum as opposed to bile in 10
of 11 paired serum and bile samples from dogs. This suggested that
bile is unlikely the source of serum CALP and is consistent with the
release of CALP from hepatocyte basolateral surfaces directly into
serum. It was concluded that serum CALP was once membrane bound and
was released by phospholipase activity into serum. Our findings are
consistent with release of CALP from the sinusoidal surfaces of
hepatocytes into serum either by endogenous GPI-PLD activity or
release by GPI-PLC followed by modification of the
phosphatidylinositol remnant in vivo.
Received 31 May 1994; accepted in final form 23 March 1995.
APS Manuscript Number G206-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.