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Differential Regulation of Phosphoinositide Phosphodiesterase Activity in Brain Membranes by Guanine Nucleotides and Calcium
Author(s) -
Gonzales Rueben A.,
Crews Fulton T.
Publication year - 1988
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1988.tb03039.x
Subject(s) - phosphodiesterase , guanine , calcium , nucleotide , chemistry , biochemistry , cyclic nucleotide phosphodiesterase , g protein , membrane , receptor , enzyme , organic chemistry , gene
We have shown previously that calcium and guanine nucleotides stimulate the activity of a phosphoinositide (PI) phosphodiesterase in membranes from rat cerebral cortex and that their effects are additive. To understand further guanine nucleotide‐ and calcium‐stimulated PI phosphodiesterase activity, we have investigated the pH sensitivity and effects of inhibitors on the two modes of stimulation. NaF stimulates PI hydrolysis in brain membranes with an EC 50 of 2 m M and a maximal effect at 10 m M , suggesting that a guanine nucleotide binding protein can regulate PI phosphodiesterase. Neomycin inhibited guanylylimidodiphosphate (GppNHp)‐stimulated PI phosphodiesterase activity in a concentration‐dependent manner, with 90% inhibition at 0.3 m M . Neomycin was not as effective at inhibiting calcium‐dependent PI hydrolysis (32% inhibition at 0.3 m M ). Chloroquine also had a greater inhibitory effect against GppNHp‐stimulated PI phospho diesterase activity compared to calcium‐dependent activity. Guanine nucleotide‐ and NaF‐dependent activations of PI phosphodiesterase were strongly pH‐dependent, with greatest stimulation observed at pH 5–6 and inhibition at more alkaline pH. Calcium‐stimulated PI hydrolysis was not as sensitive to changes in pH and had a peak of activity at pH 9. Our findings of different pH optima and differential sensitivity to inhibitors suggest that calcium and guanine nucleotides may regulate PI phosphodiesterase in rat cortical membranes through independent mechanisms. Key Words: G‐proteins—Calcium—Phosphoinositides—Membranes—Phosphoinositide phosphodiesterase—Brain. Gonzales R. A. and Crews F. T . Differential regulation of phosphoinositide phosphodiesterase activity in brain membranes by guanine nucleotides and calcium. J. Neurochem . 50 , 1522–1528 (1988).