Abstract
The effects of sodium fluoride upon basal and agonist-stimulated inositol phospholipid breakdown have been investigated in rat brain miniprisms. NaF concentration dependently increased basal inositol phospholipid breakdown, with a maximum effect being seen at 20 mM. NaF reduced the inositol phospholipid breakdown responses to stimulation by carbachol, noradrenaline, serotonin and quisqualate, but not to the stimulation produced by raising the assay [K +] from 6 to 18 mM. More detailed study demonstrated NaF to have a ‘levelling’ effect, reducing all InsP/(Lipid + InsP) valuesn 0.15 (i.e. produce by carbachol at raised [K +], noradrenline and by 50 mM K +) to about this Time-course experiments indicated that NaF treatment reduced the rate of carbachol-stimulated inositol phospholipid breakdown up to this InsP/(Lipid + InsP) level and thereafter blocked further breakdown. Inhibitory effects upon carbachol-stimulated inositol phospholipid phosphoinositides from [ 3H]myo-inositol, NaF reduced the total Lipid + InsP labelling by about 20%. NaF in addition inhibits the activity of Ins(1,4)P 2-phosphatase in cerebral cortical homogenates. It is concluded that fluoride ions inhibit agonist-stimulated inositol phospholipid breakdown via actions not only on G-proteins but also on phosphoinositide-specific phospholipase C substrate availability.
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