A Single Amino Acid Change in CaV1.2 Channels Eliminates the Permeation and Gating Differences Between Ca2+ and Ba2

• Published in: The Journal of membrane biology 2010-02, Vol.233 (1-3), p.23-33
• Main Authors: Li, Zhe, Wang, Xianming, Gao, Guofeng, Qu, Dongmei, Yu, Buwei, Huang, Congxin, Elmslie, Keith S., Peterson, Blaise Z.
• Format: Article
• Language: English
• Subjects: Amino acids; Biochemistry; Biomedical and Life Sciences; Cellular biology; Human Physiology; Life Sciences; Membranes; Mutation
• ISSN: 0022-2631; 1432-1424
• DOI: 10.1007/s00232-009-9221-1

Glutamate scanning mutagenesis was used to assess the role of the calcicludine binding segment in regulating channel permeation and gating using both Ca 2+ and Ba 2+ as charge carriers. As expected, wild-type Ca V 1.2 channels had a Ba 2+ conductance ~2× that in Ca 2+ (G Ba /G Ca  = 2) and activation was ~10 mV more positive in Ca 2+ vs. Ba 2+ . Of the 11 mutants tested, F1126E was the only one that showed unique permeation and gating properties compared to the wild type. F1126E equalized the Ca V 1.2 channel conductance (G Ba /G Ca  = 1) and activation voltage dependence between Ca 2+ and Ba 2+ . Ba 2+ permeation was reduced because the interactions among multiple Ba 2+ ions and the pore were specifically altered for F1126E, which resulted in Ca 2+ -like ionic conductance and unitary current. However, the high-affinity block of monovalent cation flux was not altered for either Ca 2+ or Ba 2+ . The half-activation voltage of F1126E in Ba 2+ was depolarized to match that in Ca 2+ , which was unchanged from that in the wild type. As a result, the voltages for half-activation and half-inactivation of F1126E in Ba 2+ and Ca 2+ were similar to those of wild-type in Ca 2+ . This effect was specific to F1126E since F1126A did not affect the half-activation voltage in either Ca 2+ or Ba 2+ . These results indicate that residues in the outer vestibule of the Ca V 1.2 channel pore are major determinants of channel gating, selectivity, and permeation.