Amino acid substitutions in the pore of the CaV1.2 calcium channel reduce barium currents without affecting calcium currents

Xianming Wang, Tudor A. Ponoran, Randall L. Rasmusson, David S. Ragsdale, Blaise Z. Peterson

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

Ba2+ currents through CaV1.2 Ca2+ channels are typically twice as large as Ca2+ currents. Replacing Phe-1144 in the pore-loop of domain III with glycine and lysine, and Tyr-1152 with lysine, reduces whole-cell GBa/GCa from 2.2 (wild-type) to 0.95, 1.21, and 0.90, respectively. Whole-cell and single-channel measurements indicate that reductions in GBa/GCa result specifically from a decrease in Ba2+ conductance and not changes in Vh or PO. Half-maximal block of ILi is increased by 3.2-, 3.8-, and 1.6-fold in Ca2+, and 3.8-, 4.2-, and 1.8-fold in Ba 2+ for F1144G, Y1152K, and F1144K, respectively. High affinity interactions of individual divalent cations to the pore are not important for determining GBa/GCa, because the fold increases in IC 50 values for Ba2+ and Ca2+ are similar. On the contrary, conductance-concentration curves indicate that GBa/G Ca is reduced because the interactions of multiple Ba2+ ions in the mutant pores are altered. The complexity of these interactions is exemplified by the anomalous mole fraction effect, which is flattened for F1144G and FY/GK but accentuated for F1144K. In summary, the physicochemical properties of the amino acid residues at positions 1144 and 1152 are crucial to the pore's ability to distinguish between multiple Ba2+ ions and Ca2+ ions.

Original languageEnglish (US)
Pages (from-to)1731-1743
Number of pages13
JournalBiophysical journal
Volume89
Issue number3
DOIs
StatePublished - Sep 2005

All Science Journal Classification (ASJC) codes

  • Biophysics

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