Reduction of Na+ enhances phosphoinositide hydrolysis and differentiates the stimulatory and inhibitory responses to quisqualate in rat brain slices

Richard S. Jope, Xiaohua Li, George C. Ormandy, Ling Song, Mary B. Williams

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


The concentration of Na+ in the incubation medium significantly influenced phosphoinositide hydrolysis induced by some, but not all, agonists in rat cerebral cortical slices. Reductions of the Na+ concentration below 120 mM resulted in incremental increases in basal and norepinephrine-stimulated accumulation of [3H]inositol monophosphate in cortical slices that had been prelabelled with [3H]inositol, and maximal responses were obtained with 0 and 5 mM Na+. In contrast, the responses to carbachol and ibotenate were similar in medium containing 120 or 5 mM Na+. In medium with 120 mM Na+, quisqualate has two effects on phosphoinositide hydrolysis in cortical slices, including a relatively weak stimulatory effect and an inhibitory modulation of the stimulation induced by norepinephrine. These two responses to quisqualate were differentially modulated by Na+; in 5 mM compared with 120 mM Na+ the stimulatory response was greatly increased and the inhibitory effect was mostly eliminated. That these were two separate events was confirmed by the use of l-BOAA (β-N-oxalyl-l-α,β-diaminopropionic acid), which reproduces the inhibitory, but not the stimulatory effect of quisqualate on phosphoinositide hydrolysis. In 5 mM Na+, inhibition by l-BOAA of norepinephrine-stimulated phosphoinositide hydrolysis was completely eliminated. These results demonstrate that a physiological concentration of Na+ maintains phosphoinositide hydrolysis at a submaximal level of sensitivity to some, but not all, agonists. The differential effects of Na+ on the stimulatory and inhibitory effects of quisqualate further substantiate the suggestion that these are two separate processes and indicate that alterations of the Na+ concentration may influence the effects of quisqualate, and other agonists, on phosphoinositide hydrolysis.

Original languageEnglish (US)
Pages (from-to)251-256
Number of pages6
JournalBrain research
Issue number1-2
StatePublished - Dec 17 1990
Externally publishedYes


  • Excitatory amino acid
  • Inositol phosphate
  • Norepinephrine
  • Quisqualate
  • Sodium-dependent

ASJC Scopus subject areas

  • Developmental Biology
  • Molecular Biology
  • Clinical Neurology
  • Neuroscience(all)


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