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Characteristics of intracellular Ca/sup 2 +/ release mediated by GTP

Conference · · Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States)
OSTI ID:6029559
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GTP (but not non-hydrolysable analogs) promotes microsomal Ca/sup 2 +/ release from several tissues provided polyethylene glycol (PEG) is present in the incubation medium. GTP-mediated Ca/sup 2 +/ release from insulinoma or rat liver microsomes is slow and proceeds only after a lag. Rapid Ca/sup 2 +/ release promoted by inositol trisphosphate occurs in microsomes from insulinoma but not liver unless GTP is present. Further experiments indicate that the effects of GTP are dependent on the ionic strength of the incubation medium, the intravesicular Ca/sup 2 +/ load, and are retained upon salt-washing or further purification of the microsomes. GTP-mediated Ca/sup 2 +/ release is halted by an excess of GTP..gamma..S added during the lag or at any stage of Ca/sup 2 +/ release indicating the continued requirement for GTP to sustain release. However, analogs do not promote Ca/sup 2 +/ re-accumulation when added after the release is complete. The relative potency with which analogs inhibit GTP-mediated Ca/sup 2 +/ release was similar to their ability to displace bound ..cap alpha../sup 32/P-GTP. 7-Methyl GTP was found to be relatively ineffective at releasing Ca/sup 2 +/ or displacing ..cap alpha../sup 32/P-GTP. PEG stimulated the rate of ..cap alpha../sup 32/P-GTP binding without affecting the equilibrium value. The lack of a similar effect on /sup 35/S-GTP-..gamma..S binding is consistent with previous studies suggesting that the step affected by PEG is GTP hydrolysis. Experiments on the purification of microsomal high affinity GTPase will be presented and the physiological relevance of this Ca/sup 2 +/ release mechanism will be assessed.
Research Organization:
Univ. of Pennsylvania, Philadelphia
OSTI ID:
6029559
Report Number(s):
CONF-870644-
Conference Information:
Journal Name: Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States) Journal Volume: 46:6
Country of Publication:
United States
Language:
English

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Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ACID ANHYDRASES
ALCOHOLS
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BODY
CALCIUM COMPOUNDS
CATIONS
CELL CONSTITUENTS
CHARGED PARTICLES
DAYS LIVING RADIOISOTOPES
DIGESTIVE SYSTEM
ENZYMES
FRACTIONATION
GLANDS
GLYCOLS
GUANYLIC ACID
HYDROLASES
HYDROXY COMPOUNDS
IONS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
LIVER
MAMMALS
MICROSOMES
NUCLEI
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC POLYMERS
ORGANOIDS
ORGANS
PHOSPHOHYDROLASES
PHOSPHORUS 32
PHOSPHORUS ISOTOPES
POLYETHYLENE GLYCOLS
POLYMERS
RADIOISOTOPES
RATS
REACTION KINETICS
RODENTS
SECRETION
SEPARATION PROCESSES
TRACER TECHNIQUES
VERTEBRATES