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2015 ; 146
(6
): 527-40
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English Wikipedia
Differential mechanisms of Cantú syndrome-associated gain of function mutations
in the ABCC9 (SUR2) subunit of the KATP channel
#MMPMID26621776
Cooper PE
; Sala-Rabanal M
; Lee SJ
; Nichols CG
J Gen Physiol
2015[Dec]; 146
(6
): 527-40
PMID26621776
show ga
Cantú syndrome (CS) is a rare disease characterized by congenital hypertrichosis,
distinct facial features, osteochondrodysplasia, and cardiac defects. Recent
genetic analysis has revealed that the majority of CS patients carry a missense
mutation in ABCC9, which codes for the sulfonylurea receptor SUR2. SUR2 subunits
couple with Kir6.x, inwardly rectifying potassium pore-forming subunits, to form
adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels, which link
cell metabolism to membrane excitability in a variety of tissues including
vascular smooth muscle, skeletal muscle, and the heart. The functional
consequences of multiple uncharacterized CS mutations remain unclear. Here, we
have focused on determining the functional consequences of three documented human
CS-associated ABCC9 mutations: human P432L, A478V, and C1043Y. The mutations were
engineered in the equivalent position in rat SUR2A (P429L, A475V, and C1039Y),
and each was coexpressed with mouse Kir6.2. Using macroscopic rubidium
((86)Rb(+)) efflux assays, we show that K(ATP) channels formed with P429L, A475V,
or C1039Y mutants enhance K(ATP) activity compared with wild-type (WT) channels.
We used inside-out patch-clamp electrophysiology to measure channel sensitivity
to ATP inhibition and to MgADP activation. For P429L and A475V mutants,
sensitivity to ATP inhibition was comparable to WT channels, but activation by
MgADP was significantly greater. C1039Y-dependent channels were significantly
less sensitive to inhibition by ATP or by glibenclamide, but MgADP activation was
comparable to WT. The results indicate that these three CS mutations all lead to
overactive K(ATP) channels, but at least two mechanisms underlie the observed
gain of function: decreased ATP inhibition and enhanced MgADP activation.