Activation of ryanodine receptors induces calcium influx in a neuroblastoma cell line lacking calcium influx factor activity

We have further characterized the Ca²⁺ signalling properties of the NG115-401L (or 401L) neuroblastoma cell line, which has served as an important cell line for investigating SOC (store-operated channel) influx pathways. These cells possess an unusual Ca²⁺ signalling phenotype characterized by the absence of Ca²⁺ influx when Ca²⁺ stores are depleted by inhibitors of SERCA (sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase). Previous studies found that Ca²⁺-store depletion does not produce a CIF (Ca²⁺ influx factor) activity in 401L cells. These observations have prompted the question whether 401L cells possess the signalling machinery that permits non-voltage-gated Ca²⁺ influx to occur. We tested the hypothesis that ryanodine-sensitive Ca²⁺ pools and activation of RyRs (ryanodine receptors) constitute a signalling pathway capable of inducing Ca²⁺ influx in 401L cells. We found that 401L cells express mRNA for RyR1 and RyR2 and that RyR activators induced Ca²⁺ release. Activation of RyRs robustly couples with Ca²⁺ influx responses in 401L cells, in sharp contrast with absence of Ca²⁺ influx when cells are treated with SERCA inhibitors. Thus it is clear that 401L cells, despite lacking depletion-induced Ca²⁺ influx pathways, express the functional components of a Ca²⁺ influx pathway under the control of RyR function. These findings further support the importance of the 401L cell line as an important cell phenotype for deciphering Ca²⁺ influx regulation.