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BIOCHEMICAL AND B!OPHYSTCAL RESEARCH COI’AWNICATIONS 224, 754—759 (1996)
AncLE NO. 1095
Are Cytoskeletal Components Invoived in the Control of Hepatio
Carnitine PaIm¡toyltransferase 1 Activity?
Guillermo Velasco,* Cristina Sánchez,* Math 3. H. Geelen,t-1 and Manuel Guzmín*
*Dgp~rgy~~~ of Biochem¿srry ¿md Molecular Biology 1, Facu.fry of Biology, Complutense Universiry,
28040-Madrid, Spain; ¿md tLaborarory of Vererinary Biochemisrry ¿md Insinue of Biomembranes
Urrechs Universiry, 35082V Urreclz 77w Nerherlands
Received luna 7, 1996
The present work was underraken to test wheter cytoslcelera¡ componenrs are involved in te control
ofrat-liver carniríne pa]miraylnansferase Y (CFI-!) ac~ry by cellular effectars. Iba núcrotubule stabilizer
taxa] abolished te changes ¡a CFI-! acrívity induced by te effectors resred. Taxol a]so prevenred OAinduced
sbrinkage of heparocyres as wdll as te enhanced release of lacrare debydrogenase fram dígitanin-
- permeabilized hepatocyres. On te basis of frs reladve sensirivity tu tautomycin and QA, te modularían
of CFI-! activity seemed tu involve masdy protein pliaspliarase 1. flese dan suggest taL te sboit-tenn
confrol of bepatic CFI-! by cellular effecrors may lavolve modularían of inreracdons berween CFI-Y and
cyroskeletai companents. © 1996 Aeadic Pztss. Inc.
Carnitine pallmitoylu-ansferase 1 (CPT-I), te mitochondrial outer membrane carnitine palmitoyltransferase,
catalyzes te pace-sett¡ng step of long-chain fatty acid transiocañon into te
mitochondrial matrix (1-3). The phosphatase inhibitor okadaic acid (OA) is able to stimulate
by up to 50% hepañc CFI-! activity as well as paimitate oxidatian (4,5). Tbis observation led
to te suggestion thai, apart fi-orn modulation of mt-livor CPT-I activity by malonyl-CoA, a
phosphorylañon-dephosphorylation mechanism might be involved in te shart-term control of
tbis enzyme (3). However, further research showed tat te increase of CPT-Iactivity observed
lxi QA-treated hepatocytes was not due to direct phosphorylation of te CPT-I enzyme, bat
may involve interactions between te mitochondriai outer membrane and extra-mitochondrial
ceil components (6).
A number of reports hayo recently described dxc existence of specific interactioxis between
te mitochondrial outer membrane and cytoskeletal elements (7-9). Lx te context of CFI’-!
regulation, QA and vanadate, which activate hepatio CPT-I (5,10), have been shown to disnapt
te cytoslceleton of heparocytes (11-13). Furthermore, CFI’-! activity is affected by changes
lix hepatocyte volumne (14), mrd several responses of hepatocytes to changes in cd volume
are dependent on micx-otubuie dynamics (15,16). Iherefore, dxc present work was undertaken
ro rest whether cytoskeletai companents may be involved lix te control of hepaúc CFI’-!
activity by OA mrd other short-term effectors of celular metabolisin.
MATERIALS AND METI-4ODS
Mala Wisrarras (250-300 g) wbich liad fice accesa ta foad and wazer were usad tzougbaurin rbis snzdy. Heparoc>ts
were ¡salmed and incubared as descúbed la (17). Ya sorne expeuiments, te osmalanry of te medíum (305 mOsm in
te normal, iso-osmaric Krebs-Henselelr bicarbanare buifer) was increasad tu 385 mOsm (byper-osmadc medium) by
cbanging te NaO concentrarían. Ibis was achieved by adding 10 ~u1of 4.0 M NaO per ml of ceil incubarían.
ASter incubarían of dic beparocytes wirh te addidons indicared ¡a cadi case, CFI-! acdvfty was rourinely daumined
in digfronin-permeabiiized beparocyres exacdy as described befare (5).
‘lo wbam canespondence sbould be addressed.
0006-291X/96 518-00
Cop>~~ 01996 by Acade,c Press. Inc.
MI ,í~u of re~odtaedou m any fom resnvS.
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