Interplay between Calmodulin and Phosphatidylinositol 4,5-Bisphosphate in Ca2+-induced Inactivation of Transient Receptor Potential Vanilloid 6 Channels |
| |
Authors: | Chike Cao Eleonora Zakharian Istvan Borbiro Tibor Rohacs |
| |
Institution: | From the Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103 |
| |
Abstract: | The epithelial Ca2+ channel transient receptor potential vanilloid 6 (TRPV6) undergoes Ca2+-induced inactivation that protects the cell from toxic Ca2+ overload and may also limit intestinal Ca2+ transport. To dissect the roles of individual signaling pathways in this phenomenon, we studied the effects of Ca2+, calmodulin (CaM), and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in excised inside-out patches. The activity of TRPV6 strictly depended on the presence of PI(4,5)P2, and Ca2+-CaM inhibited the channel at physiologically relevant concentrations. Ca2+ alone also inhibited TRPV6 at high concentrations (IC50 = ∼20 μm). A double mutation in the distal C-terminal CaM-binding site of TRPV6 (W695A/R699E) essentially eliminated inhibition by CaM in excised patches. In whole cell patch clamp experiments, this mutation reduced but did not eliminate Ca2+-induced inactivation. Providing excess PI(4,5)P2 reduced the inhibition by CaM in excised patches and in planar lipid bilayers, but PI(4,5)P2 did not inhibit binding of CaM to the C terminus of the channel. Overall, our data show a complex interplay between CaM and PI(4,5)P2 and show that Ca2+, CaM, and the depletion of PI(4,5)P2 all contribute to inactivation of TRPV6. |
| |
Keywords: | Calcium Calcium Channels Calmodulin Inositol Phospholipid Ion Channels Phosphatidylinositol Signaling TRP Channels PIP2 |
|
|