Lithium inhibits muscarinic-receptor-stimulated inositol tetrakisphosphate accumulation in rat cerebral cortex.
The effects of Li+ on carbachol-stimulated phosphoinositide metabolism were examined in rat cerebral-cortex slices labelled with myo-[2-3H]inositol. The muscarinic agonist carbachol evoked an enhanced steady-state accumulation of [3H]inositol monophosphate ([3H]InsP1), [3H]inositol bisphosphate ([3H]InsP2), [3H]inositol 1,3,4-trisphosphate ([3H]Ins(1,3,4)P3), [3H]inositol 1,4,5-trisphosphate ([3H]Ins(1,4,5)P3) and [3H]inositol tetrakisphosphate ([3H]InsP4). Li+ (5 mM), after a 10 min lag, severely attenuated carbachol-stimulated [3H]InsP4 accumulation while simultaneously potentiating accumulation of both [3H]InsP1 and [3H]InsP2 and, at least initially, of [3H]Ins(1,3,4)P3. These data are consistent with inhibition of inositol mono-, bis- and 1,3,4-tris-phosphate phosphatases to different degrees by Li+ in brain, but are not considered to be completely accounted for in this way. Potential direct and indirect mechanisms of the inhibitory action of Li+ on [3H]InsP4 accumulation are considered. The present results stress the complex action of Li+ on cerebral inositol metabolism and indicate that more complex mechanisms than are yet evident may regulate this process.
Batty
I
I
Department of Pharmacology and Therapeutics, University of Leicester, U.K.
Nahorski
S R
SR
D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism; D013403:Sugar Phosphates / Q000378:metabolism*
D007295:Inositol Phosphates; D011976:Receptors, Muscarinic; D013403:Sugar Phosphates; D008094:Lithium