Differential Effects of Lithium on Muscarinic Cholinoceptor-Stimulated CMP-Phosphatidate Accumulation in Cerebellar Granule Cells, CHO-M3 Cells, and SH-SY5Y Neuroblastoma Cells

Abstract: The ability of lithium to potentiate muscarinic cholinoceptor-stimulated CMP-phosphatidate (CMP.PA) accumulation has been examined in various cells in which muscarinic cholinoceptor agonists evoke a phosphoinositide response. Cell types examined include rat cerebellar granule cells, Chinese hamster ovary cells transfected to express the human muscarinic M3 receptor (CHO-M3 cells), and SH-SY5Y neuroblastoma cells. Neither carbachol (1 m M ) nor lithium (10 m M ) caused significant increases in CMP.PA accumulation in rat cerebellar granule cells; however, when added together for 20 min a linear 17-fold increase over basal levels was observed. The increase was dependent on the concentration of carbachol and lithium present, and the effect could be reversed by addition of exogenous myo -inositol (10 m M ). Addition of carbachol alone to CHO-M3 cells caused a five-fold increase in CMP.PA accumulation. In the presence of lithium, a 70-fold increase was observed at 20 min after carbachol plus lithium addition. This latter response was concentration dependent and could be abolished by preincubation in the presence of 10 m M myo -inositol. In contrast, whereas carbachol elicited a three-fold increase in CMP.PA accumulation in SH-SY5Y neuroblastoma cells, which reached a plateau 10 min after agonist addition, the response could neither be augmented by addition of lithium nor inhibited by addition of myo -inositol. These results emphasise that the ability of lithium to affect agonist-stimulated CMP.PA accumulation is not simply a function of stimulus strength, but is also crucially dependent on the intracellular concentration of inositol.