Essential control of an endothelial cell I_SOC by the spectrin membrane skeleton

Mechanism(s) underlying activation of store-operated Ca²⁺ entry currents, I_SOC, remain incompletely understood. F-actin configuration is an important determinant of channel function, although the nature of interaction between the cytoskeleton and I_SOC channels is unknown. We examined whether the spectrin membrane skeleton couples Ca²⁺ store depletion to Ca²⁺ entry. Thapsigargin activated an endothelial cell I_SOC (−45 pA at −80 mV) that reversed at +40 mV, was inwardly rectifying when Ca²⁺ was the charge carrier, and was inhibited by La³⁺ (50 μM). Disruption of the spectrin–protein 4.1 interaction at residues A207-V445 of βSpIIΣ1 decreased the thapsigargin-induced global cytosolic Ca²⁺ response by 50% and selectively abolished the endothelial cell I_SOC, without altering activation of a nonselective current through cyclic nucleotide–gated channels. In contrast, disruption of the spectrin–actin interaction at residues A47-K186 of βSpIIΣ1 did not decrease the thapsigargin-induced global cytosolic Ca²⁺ response or inhibit I_SOC. Results indicate that the spectrin–protein 4.1 interaction selectively controls I_SOC, indicating that physical coupling between calcium release and calcium entry is reliant upon the spectrin membrane skeleton.