Complex relationship between Ins(1,4,5)P-3 accumulation and Ca2+-signalling in a human neuroblastoma revealed by cellular differentiation

1 Differentiation of SH-SY5Y neuroblastoma cells induces morphological and biochemical changes consistent with a more neuronal phenotype. These cells may therefore provide a model for studying phenomena such as signal transdu ction in a neuronal context whilst retaining the advantages of a homogenous cell population expressing a well characterized array of G-protein coupled receptors. 2 This study examined the effects of differentiating SH-SY5Y cells on musca rinic- and bradykinin-receptor-mediated phosphoinositide and Ca2+ signallin g. Retinoic acid (LD mu M, 6 days) along with a lowered serum concentration produced phenotypic changes consistent with differentiation including redu ced proliferation and increased neurite outgrowth. 3 Differentiation increased the magnitude and potency of rapid Ins(1,4,5)P- 3 responses to a full muscarinic receptor agonist. Bradykinin receptor-medi ated Ins(1,4,5)P-3 signalling was also potentiated following differentiatio n. Determination of agonist-evoked accumulation of [H-3]-inositol phosphate s under lithium-block demonstrated these changes reflected enhanced phospho lipase C activity which is consistent with observed increases in the expres sion of muscarinic and bradykinin receptors. 4 Despite the marked alterations in Ins(1,4,5)P-3 signalling following diff erentiation, elevations of intracellular [Ca2+] were totally unaltered. Thu s, in SH-SY5Y cells, the relationship between the elevations of Ins(1,4,5)P -3 and intracellular [Ca2+] is agonist dependent and affected by the state of differentiation. This demonstrates that mechanisms other than the measur ed increase in Ins(1,4,5)P-3 regulate the elevation of intracellular [Ca2+] .