The presence of a protein activator of sarcolemmal polyphosphoinositide phospholipase C in cardiac cytosol

Journal Article · Sun Jan 01 04:00:00 EST 1989 · Proceedings of the Society for Experimental Biology and Medicine; (USA)

OSTI ID:7068626

Quist, E E; Kriewaldt, S D; Powell, P B ^[1]

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1. Texas College of Osteopathic Medicine, Fort Worth (USA)

To study polyphosphoinositide phospholipase (PL) C, isolated sarcolemmal membranes were preincubated with Mg({sup 32}P)-ATP to label phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-diphosphate (PIP{sub 2}). After washing, PLC activity was determined by measuring the release of {sup 32}P-labeled inositol diphosphate (IP{sub 2}) and/or inositol trisphospate (IP{sub 3}) from membrane PIP and PIP{sub 2} during incubation at 25{degree}C and pH 7.4. Increasing concentrations of Ca{sup 2+} (0-100 {mu}M) increased IP{sub 2} by 100% over the 0 Ca{sup 2+} control levels. Ca{sup 2+} dependent PLC hydrolyzed both PIP and PIP{sub 2} with apparent D{sub A}'s of approximately 0.5 and 70 {mu}M. Addition of dialyzed cytosol further increased IP{sub 2} release by 250% without affecting the K{sub A}'s for Ca{sup 2+} activation. The cytosolic activator was partially purified by DEAE Sephacel chromatography was heat labile and sensitive to trypsin pretreatment identifying it as a protein. In contrast, 10 mM NaF increased the Ca{sup 2+} affinity for PLC 2-fold. These results show that cardiac sarcolemma possess a membrane bound Ca{sup 2+} dependent PLC activity which is regulated by a cytosolic protein activator and a G protein. The cytosolic activator would potentially amplify the amount of sarcolemmal polyphosphoinositides hydrolyzed by PLC in response to muscarinic receptor activation by acetylcholine. In addition, activation of PLC by NaF or other G protein activators could result from increasing the Ca{sup 2+} affinity of PLC to physiological intracellular Ca{sup 2+} levels.

• OSTI ID: 7068626
• Journal Information: Proceedings of the Society for Experimental Biology and Medicine; (USA), Journal Name: Proceedings of the Society for Experimental Biology and Medicine; (USA) Vol. 191:1; ISSN PSEBA; ISSN 0037-9727
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH METAL COMPOUNDS
ATP
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BODY
CALCIUM COMPOUNDS
CARBOHYDRATES
CARBOXYLESTERASES
CARDIOVASCULAR SYSTEM
DAYS LIVING RADIOISOTOPES
ENZYME ACTIVITY
ENZYMES
ESTERASES
HEART
HYDROLASES
INOSITOLS
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
LIPASES
MONOSACCHARIDES
NUCLEI
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANS
PHOSPHORUS 32
PHOSPHORUS ISOTOPES
RADIOISOTOPES
SACCHARIDES
TRACER TECHNIQUES