The activity of persistent Ca2+ sparklets, which are characterized by longer and more frequent channel open events than low-activity sparklets, contributes substantially to steady-state Ca2+ entry under physiological conditions. Here, we addressed two questions related to the regulation of Ca2+ sparklets by PKC-α and c-Src, both of which increase whole cell Cav1.2 current: 1) Does c-Src activation enhance persistent Ca2+ sparklet activity? 2) Does PKC-α activate c-Src to produce persistent Ca2+ sparklets? With the use of total internal reflection fluorescence microscopy, Ca2+ sparklets were recorded from voltage-clamped tsA-201 cells coexpressing wild-type (WT) or mutant Cav1.2c (the neuronal isoform of Cav1.2) constructs ± active or inactive PKC-α/c-Src. Cells expressing Cav1.2c exhibited both low-activity and persistent Ca2+ sparklets. Persistent Ca2+ sparklet activity was significantly reduced by acute application of the c-Src inhibitor PP2 or coexpression of kinase-dead c-Src. Cav1.2c constructs mutated at one of two COOH-terminal residues (Y2122F and Y2139F) were used to test the effect of blocking putative phosphorylation sites for c-Src. Expression of Y2122F but not Y2139F Cav1.2c abrogated the potentiating effect of c-Src on Ca2+ sparklet activity. We could not detect a significant change in persistent Ca2+ sparklet activity or density in cells coexpressing Cav1.2c + PKC-α, regardless of whether WT or Y2122F Cav1.2c was used, or after PP2 application, suggesting that PKC-α does not act upstream of c-Src to produce persistent Ca2+ sparklets. However, our results indicate that persistent Ca2+ sparklet activity is promoted by the action of c-Src on residue Y2122 of the Cav1.2c COOH terminus.
Differential Effects of CC Chemokines on CC Chemokine Receptor 5 (CCR5) Phosphorylation and Identification of Phosphorylation Sites on the CCR5 Carboxyl Terminus
