Guanine nucleotides stimulate phosphoinositide breakdown in permeabilized platelets
Human platelets were preincubated with myo-(/sup 3/H)inositol in the presence of Mn/sup 2 +/, permeabilized by high voltage electric discharges and isolated by gel filtration. After equilibration with ATP, Ca/sup 2 +/ buffers and 0-100 ..mu..M GTP..gamma..S at 0/sup 0/C, the platelets were incubated for 0 to 5 min at 25/sup 0/C. Incubation alone led to a Ca/sup 2 +/-independent conversion of (/sup 3/H)phosphatidylinositol to (/sup 3/H)phosphatidylinositol 4-phosphate (PIP). In addition, GTP..gamma..S (100 ..mu..M) caused a 30-40% loss of (/sup 3/H)phosphatidylinositol 4,5-bisphosphate (PIP/sub 2/) in the presence of 0.1-1.0 ..mu..M Ca/sup 2 +//sub free/. This was fully accounted for by the progressive accumulation of inositol monophosphate (IP) and inositol bisphosphate (IP/sub 2/) in a ratio of 3:1. After 5 min, GTP..gamma..S had increased IP by >8-fold and IP/sub 2/ by >4-fold. Only traces of inositol trisphosphate (IP/sub 3/) were detected. Li/sup +/ (10 mM) increased IP/sub 2/ accumulation at the expense of IP, indicating conversion of the former to the latter, but did not increase IP/sub 3/. Unlabelled IP/sub 3/ (400 ..mu..M) reduced the intracellular degradation of 14 ..mu..M (/sup 32/P)IP/sub 3/ added to permeabilized platelets by 55% but did not decrease (/sup 3/H)IP/sub 2/ formation or increase (/sup 3/H)IP/sub 3/ in GTP..gamma..S-stimulated platelets. Thrombin (2 units/ml), in the presence of 10 ..mu..M GTP, stimulated the formation of inositol phosphates in a manner qualitatively similar to GTP..gamma..S. These results suggest that, in platelets, a guanine nucleotide-binding protein can activate breakdown of PIP/sub 2/ to IP/sub 2/ and diacylglycerol by a pathway that does not involve IP/sub 3/ formation.
- Research Organization:
- McMaster Univ., Hamilton, Ontario
- OSTI ID:
- 7108687
- Report Number(s):
- CONF-8606151-; TRN: 86-039051
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Vol. 45:6; Conference: 76. annual meeting of the Federation of American Society for Experimental Biology, Washington, DC, USA, 8 Jun 1986
- Country of Publication:
- United States
- Language:
- English
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GUANINE
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CATIONS
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MAN
MANGANESE COMPOUNDS
NUCLEOTIDES
PHOSPHORUS 32
TRACER TECHNIQUES
TRITIUM COMPOUNDS
AMINES
ANIMALS
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CHARGED PARTICLES
DAYS LIVING RADIOISOTOPES
ESTERS
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
INOSITOLS
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LABELLED COMPOUNDS
LIGHT NUCLEI
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550201* - Biochemistry- Tracer Techniques