L-type calcium channel -subunit and protein kinase inhibitors modulate Rem-mediated regulation of current

Crump, Shawn M., Robert N. Correll, Elizabeth A. Schroder, William C. Lester, Brian S. Finlin, Douglas A. Andres, and Jonathan Satin. L-type calcium channel -subunit and protein kinase inhibitors modulate Rem-mediated regulation of current. Am J Physiol Heart Circ Physiol 291: H1959–H1971, 2006. First published April 28, 2006; doi:10.1152/ajpheart.00956.2005.—Cardiac voltage-gated L-type Ca channels (CaV) are multiprotein complexes, including accessory subunits such as CaV 2 that increase current expression. Recently, members of the Rad and Gem/Kir-related family of small GTPases have been shown to decrease current, although the mechanism remains poorly defined. In this study, we evaluated the contribution of the L-type Ca channel -subunit (CaV1.2) to CaV 2-Rem inhibition of Ca channel current. Specifically, we addressed whether protein kinase A (PKA) modulation of the Ca channel modifies CaV 2-Rem inhibition of Ca channel current. We first tested the effect of Rem on CaV1.2 in human embryonic kidney 293 (HEK-293) cells using the whole cell patch-clamp configuration. Rem coexpression with CaV1.2 reduces Ba current expression under basal conditions, and CaV 2a coexpression enhances Rem block of CaV1.2 current. Surprisingly, PKA inhibition by 133 nM H-89 or 50 M Rp-cAMP-S partially relieved the Rem-mediated inhibition of current activity both with and without CaV 2a. To test whether the H-89 action was a consequence of the phosphorylation status of CaV1.2, we examined Rem regulation of the PKA-insensitive CaV1.2 serine 1928 (S1928) to alanine mutation (CaV1.2-S1928A). CaV1.2-S1928A current was not inhibited by Rem and when coexpression with CaV 2a was not completely blocked by Rem coexpression, suggesting that the phosphorylation of S1928 contributes to Rem-mediated Ca channel modulation. As a model for native Ca channel complexes, we tested the ability of Rem overexpression in HIT-T15 cells and embryonic ventricular myocytes to interfere with native current. We find that native current is also sensitive to Rem block and that H-89 pretreatment relieves the ability of Rem to regulate Ca current. We conclude that Rem is capable of regulating L-type current, that release of Rem block is modulated by cellular kinase pathways, and that the CaV1.2 COOH terminus contributes to Rem-dependent channel inhibition.