Calcineurin upregulates local Ca2+ signaling through ryanodine receptor-1 in airway smooth muscle cells

Abstract

Local Ca2+ signals (Ca2+ sparks) play an important role in multiple cellular functions in airway smooth muscle cells (ASMCs). Protein kinase Cϵ is known to downregulate ASMC Ca2+ sparks and contraction; however, no complementary phosphatase has been shown to produce opposite effects. Here, we for the first time report that treatment with a specific calcineurin (CaN) autoinhibitory peptide (CAIP) to block CaN activity decreases, whereas application of nickel to activate CaN increases, Ca2+ sparks in both the presence and absence of extracellular Ca2+. Treatment with xestospogin-C to eliminate functional inositol 1,4,5-trisphosphate receptors does not prevent CAIP from inhibiting local Ca2+ signaling. However, high ryanodine treatment almost completely blocks spark formation and prevents the nickel-mediated increase in sparks. Unlike CAIP, the protein phosphatase 2A inhibitor endothall has no effect. Local Ca2+ signaling is lower in CaN catalytic subunit Aα gene knockout (CaN-Aα−/−) mouse ASMCs. The effects of CAIP and nickel are completely lost in CaN-Aα−/− ASMCs. Neither CAIP nor nickel produces an effect on Ca2+ sparks in type 1 ryanodine receptor heterozygous knockout (RyR1−/+) mouse ASMCs. However, their effects are not altered in RyR2−/+ or RyR3−/− mouse ASMCs. CaN inhibition decreases methacholine-induced contraction in isolated RyR1+/+ but not RyR1−/+ mouse tracheal rings. Supportively, muscarinic contractile responses are also reduced in CaN-Aα−/+ mouse tracheal rings. Taken together, these results provide novel evidence that CaN regulates ASMC Ca2+ sparks specifically through RyR1, which plays an important role in the control of Ca2+ signaling and contraction in ASMCs.