Discrete influx events refill depleted Ca 2+ stores in a chick retinal neuron

The depletion of ER Ca 2+ stores, following the release of Ca 2+ during intracellular signalling, triggers the Ca 2+ entry across the plasma membrane known as store‐operated calcium entry (SOCE). We show here that brief, local [Ca 2+ ] i increases (motes) in the thin dendrites of cultured retinal amacrine cells derived from chick embryos represent the Ca 2+ entry events of SOCE and are initiated by sphingosine‐1‐phosphate (S1P), a sphingolipid with multiple cellular signalling roles. Externally applied S1P elicits motes but not through a G protein‐coupled membrane receptor. The endogenous precursor to S1P, sphingosine, also elicits motes but its action is suppressed by dimethylsphingosine (DMS), an inhibitor of sphingosine phosphorylation. DMS also suppresses motes induced by store depletion and retards the refilling of depleted stores. These effects are reversed by exogenously applied S1P. In these neurons formation of S1P is a step in the SOCE pathway that promotes Ca 2+ entry in the form of motes.