© 1998 American Heart Association, Inc.
Original Contributions |
Reconstituted Human Cardiac KATP Channels
Functional Identity With the Native Channels From the Sarcolemma of Human Ventricular Cells
From the Departments of Cell Biology (A.P.B., G.G., J.B.) and Medicine (L.A.-B.), Baylor College of Medicine, Houston, Tex.
Correspondence to Andrey P. Babenko, MD, PhD, Department of Cell Biology, Baylor College of Medicine, 112C, 1 Baylor Plaza, Houston, TX 77030. E-mail ababenko{at}bcm.tmc.edu
Abstract—ATP-sensitive potassium
(KATP) channels in striated myocytes are
heteromultimers of KIR6.2, a weak potassium inward
rectifier, plus SUR2A, a low-affinity sulfonylurea receptor. We have
cloned human KIR6.2 (huKIR6.2) and a huSUR2A
that corresponds to the major, full-length splice variant identified by
polymerase chain reaction analysis of human cardiac poly
A+ mRNA. ATP- and glibenclamide-sensitive K+
channels were produced when both subunits were coexpressed in COSm6 and
Chinese hamster ovary cells lacking endogenous
KATP channels, but not when huSUR2A or huKIR6.2
were transfected alone. Recombinant channels activated by
metabolic inhibition in cell-attached configuration or in
inside-out patches with ATP-free internal solution were compared with
sarcolemmal KATP channels in human ventricular
cells. The single-channel conductance of 
80 pS measured at -40 mV
in quasi-symmetrical 150 mmol/L K+ solutions, the
intraburst kinetics that were dependent on K+ driving
force, and the weak inward rectification were indistinguishable for
both channels. Similar to the native channels,
huSUR2A/huKIR6.2 recombinant channels were inhibited by ATP
at quasi-physiological free Mg2+
(0.7 mmol/L) or in the absence of Mg2+, with an
apparent IC50 of 20 µmol/L and a pseudo-Hill
coefficient of 1. They were "refreshed" by MgATP and stimulated
by ADP in the presence of Mg2+ when inhibited by ATP. The
huSUR2A/huKIR6.2 channels were stimulated by cromakalim and
pinacidil in the presence of ATP and Mg2+ but were
insensitive to diazoxide. The results suggest that reconstituted
huSUR2A/huKIR6.2 channels represent
KATP channels in sarcolemma of human
cardiomyocytes and are an adequate experimental model with
which to examine structure-function relationships, molecular
physiology, and pharmacology of these channels from human heart.
Key Words: ATP-sensitive K+ channel • KIR6.2 • SUR2A • isoform • splice variant
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