Format

Send to

Choose Destination
See comment in PubMed Commons below
Biophys J. 2003 Jun;84(6):3679-89.

Pore- and state-dependent cadmium block of I(Ks) channels formed with MinK-55C and wild-type KCNQ1 subunits.

Author information

1
Department of Pediatrics, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.

Abstract

Human MinK and KCNQ1 subunits assemble to form I(Ks) channels. When MinK position 55 is mutated to cysteine (MinK-55C), I(Ks) channels can be blocked by external cadmium (Cd(2+)). We have supported a pore-associated location for MinK-55C because Cd(2+) block is sensitive to voltage, permeant ions on the opposite side of the membrane (trans-ions), and external tetraethylammonium (TEA), an I(Ks) pore-blocker. Two recent reports argue that MinK-55C is distant from the pore: one finds TEA does not affect Cd(2+) block if channels are formed with a KCNQ1 mutant (K318I, V319Y) that increases TEA affinity; the second proposes that Cd(2+) binds between MinK-55C and a cysteine in KCNQ1 that is posited to lie toward the channel periphery. Here, these discrepancies are considered. First, Cd(2+) block of MinK-55C channels formed with wild-type KCNQ1 is shown to depend not only on voltage and trans-ions but state (showing decreased on-rate with increased open time and blocker trapping on channel closure). Conversely, MinK-55C channels with K318I, V319Y KCNQ1 are found to demonstrate Cd(2+) block that is independent of voltage, trans-ions and state (and to have a lower unitary conductance): thus, the KCNQ1 mutations alter the process under study, yielding Cd(2+) inhibition that is pore-independent and, perforce, TEA-insensitive. Second, MinK-55C channels are found to remain sensitive to Cd(2+) despite mutation of any single native cysteine in KCNQ1 or all nine simultaneously; this suggests no KCNQ1 cysteine binds Cd(2+) and can serve to localize MinK-55C. Despite many concerns that are enumerated, we remain obliged to conclude that Cd(2+) enters and leaves the pore to reach MinK-55C, placing that residue in or near the pore.

PMID:
12770875
PMCID:
PMC1302951
DOI:
10.1016/S0006-3495(03)75097-8
[Indexed for MEDLINE]
Free PMC Article
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for Elsevier Science Icon for PubMed Central
    Loading ...
    Support Center